Multiple Time Constants Research Articles

(Invited) Electrochemical Impedance Spectroscopy of Reinforced Concrete

Electrochemical impedance spectroscopy (EIS) is an effective method for assessing interfacial parameters within systems that have consistent electrode-electrolyte interface impedance and for which a uniform distribution of current can be acheived. The application of EIS to reinforced concrete presents a myriad of challenges due to various factors such as moisture content, interfacial porosity, and the presence of corrosion products. These complexities make it imperative to clearly define the limitations in the application of EIS to corrosion assessment of steel in concrete. The impedance response may include multiple time constants, forming a Nyquist display comprising capacitive loops with various degrees of depression and overlap. Despite numerous proposed models1,2,3 attempting to account for these responses, there is a lack of widely adopted models capable of characterizing the steel-concrete interface across different stages of corrosion. Complicating matters further, early corrosion stages are often nonuniform, making it difficult to discern whether the observed multiple time constants reflect processes occurring uniformly across the surface or at distinct locations along it. In the first part of the presentation, the challenges associated with analyzing the impedance of steel within concrete will be described, including an in-depth exploration of factors such as geometry-induced frequency dispersion and the influence of localized forms of corrosion on impedance responses.4 The second part of the presentation will explore the use of bipolar electrochemical impedance spectroscopy (BPEIS) as a potential solution for field applications of corrosion assessment where direct electrical contact with the reinforcement may not be feasible. BPEIS is a non-contact method of which an electrically conductive material within an electrolyte is indirectly polarized with the goal of probing the interfacial impedance of the embedded material.5 An application example of monitoring of corrosion in post-tensioned tendons will be provided to validate the efficacy of BPEIS in evaluating corrosion rate and changes in cementitious material resistivity. Despite the challenges associated with isolating the true interface impedance, the method demonstrates reliability in assessing the corrosion state of the embedded reinforcement. John, D. G., P. C. Searson, and J. L. Dawson. "Use of AC impedance technique in studies on steel in concrete in immersed conditions." British Corrosion Journal 16, no. 2 (1981): 102-106.Dhouibi-Hachani, Leila, et al. "Comparing the steel-concrete interface state and its electrochemical impedance." Cement and Concrete Research 26.2 (1996): 253-266.Andrade, C., L. Soler, C. Alonso, X. R. Nóvoa, and M. Keddam. "The importance of geometrical considerations in the measurement of steel corrosion in concrete by means of AC impedance." Corrosion Science 37, no. 12 (1995): 2013-2023.Alexander, Christopher L., Bernard Tribollet, and Mark E. Orazem. "Influence of micrometric-scale electrode heterogeneity on electrochemical impedance spectroscopy." Electrochimica Acta201 (2016): 374-379.Alexander, Christopher L., and Mark E. Orazem. "Indirect electrochemical impedance spectroscopy for corrosion detection in external post-tensioned tendons: 1. Proof of concept." Corrosion Science 164 (2020): 108331.

Tuning ultrafast demagnetization dynamics in FePdPt ternary alloy films: the role of spin–orbit coupling

The influence of spin–orbit coupling (SOC) on ultrafast demagnetization dynamics is still an obscure issue. Ferromagnetic ternary alloy film containing Platinum element has the advantage that SOC strength can be regulated flexibly by varying the component ratio, thus is an excellent platform for investigating the dynamical effect of SOC. Here the fluence and component dependences of ultrafast demagnetization dynamics in ternary alloy L10-Fe0.5(Pd1-xPtx)0.5 films are studied by using time-resolved magneto-optical Kerr spectroscopy. An excitation-fluence dependent transition of demagnetization dynamics shows the Elliott-Yafet (EY) spin-flip scattering as the dominant mechanism of ultrafast demagnetization. We analyze the dynamics by a compatible fitting model and extract multiple characteristic time constants. It is clearly demonstrated that the gradual enhancement of SOC in fact decreases the spin-flip scattering and slow down the demagnetization process. We further show that the demagnetization time τm scales with the SOC strength ξ approximately under a dependence of τm∝ξ1/3, while a linear dependence exists between the spin–lattice relaxation time τs-l and ξ-6. These findings clarify the role of SOC in EY-dominated demagnetization dynamics and demonstrate an approach for tuning the speeds and duration of ultrafast demagnetization by regulating SOC strength.

Study on Lifetime Modeling of IGBT Modules Considering Electric Frequency Influence Mechanism

Affected by the randomness of the wind speed, the output electric frequency (0 20Hz) of the rotor-side converter does not match the thermal time constant (about 100ms) of IGBT modules, which causes the different junction temperature stress. It leads that it is difficult for the traditional lifetime model to reflect the influence of multi-time constant thermal load and result in inaccurate reliability evaluation. Aiming at the characteristics of wind turbine-side converters bearing thermal loads with multiple time constants, this paper studies the influence mechanism of electric frequency on the reliability of IGBT modules through a multi-physics simulation model and power cycling tests, and an improved lifetime model considering the influence of frequency parameters is proposed. Finally, an example analysis of the reliability evaluation of the DFIG rotor side converter is carried out. This paper is intended for the health management of converter systems and is supposed to be in service reliably.

The effects of broadband elicitor duration on a psychoacoustic measure of cochlear gain reduction.

Physiological and psychoacoustic studies of the medial olivocochlear reflex (MOCR) in humans have often relied on long duration elicitors (>100 ms). This is largely due to previous research using otoacoustic emissions (OAEs) that found multiple MOCR time constants, including time constants in the 100s of milliseconds, when elicited by broadband noise. However, the effect of the duration of a broadband noise elicitor on similar psychoacoustic tasks is currently unknown. The current study measured the effects of ipsilateral broadband noise elicitor duration on psychoacoustic gain reduction estimated from a forward-masking paradigm. Analysis showed that both masker type and elicitor duration were significant main effects, but no interaction was found. Gain reduction time constants were ∼46 ms for the masker present condition and ∼78 ms for the masker absent condition (ranging from ∼29 to 172 ms), both similar to the fast time constants reported in the OAE literature (70-100 ms). Maximum gain reduction was seen for elicitor durations of ∼200 ms. This is longer than the 50-ms duration which was found to produce maximum gain reduction with a tonal on-frequency elicitor. Future studies of gain reduction may use 150-200 ms broadband elicitors to maximally or near-maximally stimulate the MOCR.

Oxygen Adsorption and Desorption Kinetics in CuO Nanowire Bundle Networks: Implications for MOx-Based Gas Sensors

Copper oxide (CuO) nanostructures have demonstrated a good chemiresistive response for the sensing of various gases. The precise sensing mechanisms of this material and, in particular, the kinetics of the response to gases and the sensor recovery remain much less investigated. For metal oxide (MOx) chemiresistive gas sensors, oxygen adsorption and desorption reactions on a material surface play a major role in the sensor kinetics, as most other gases react with oxygen on the sensor surface in order to provide the sensing signal, and nanoscale materials are known to achieve faster response. Here we investigate the oxygen adsorption and desorption kinetics on CuO nanowire bundle (NWB) networks by analyzing the electrical response and recovery curves of sensing devices exposed to oxygen. The observation of multiple time constants for the response and recovery curves led us to discuss the various potential mechanisms related to surface reaction kinetics and diffusion of oxygen species. By comparing the reaction rate constants and diffusion constants extracted from the obtained time constants, we conclude that the diffusion of oxygen defects into the material might be the main reason for the observed large time constants. Surprisingly, we observe that the sensor devices based on as-deposited materials show 4–16 times faster response and recovery as compared to devices after being annealed, depending on the temperature. By comparing this result with detailed characterization using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, we discuss the role of the junctions between nanostructures in the network and of the hydroxylated CuO surface to explain this result. Our investigation on the kinetics of adsorption and desorption of oxygen of CuO NWB provides a direct understanding of the general response of the sensor and will be useful in order to further understand and optimize these materials for the sensing of various gases.

Normalized Dynamic Characterization and Application of Multiple Heat Storage Materials Based on Standard Thermal Resistance

Based on the standard thermal resistance and the heat current method, the transient heat transfer thermal resistance between the heat storage material and the heat transfer fluid is deduced. Through analog circuit analysis method, the transient heat current model and dynamic response time constant of heat storage-heat exchange processes are obtained. Based on this model, the node temperature is introduced for refining the heat transfer thermal resistance, and the transient heat current model of the third-order circuit coupled with the heat storage and heat transfer processes is obtained. Through numerical simulation verification and application comparison analysis, it is found that the normalized dynamic model based on multiple time constants is feasible to characterize the dynamic characteristics of heat storage materials, and can directly compare and analyze different heat exchange and heat storage materials. The case study found that when exchanging heat with solid heat storage materials, the dynamic heat exchange capacity of liquid metal is better than that of molten salt, while the heat exchange between air and ceramic materials reaches a steady state faster than that of water vapor and CO₂.

Controlling Clinical States Governed by Different Temporal Dynamics With Closed-Loop Deep Brain Stimulation: A Principled Framework.

Closed-loop strategies for deep brain stimulation (DBS) are paving the way for improving the efficacy of existing neuromodulation therapies across neurological disorders. Unlike continuous DBS, closed-loop DBS approaches (cl-DBS) optimize the delivery of stimulation in the temporal domain. However, clinical and neurophysiological manifestations exhibit highly diverse temporal properties and evolve over multiple time-constants. Moreover, throughout the day, patients are engaged in different activities such as walking, talking, or sleeping that may require specific therapeutic adjustments. This broad range of temporal properties, along with inter-dependencies affecting parallel manifestations, need to be integrated in the development of therapies to achieve a sustained, optimized control of multiple symptoms over time. This requires an extended view on future cl-DBS design. Here we propose a conceptual framework to guide the development of multi-objective therapies embedding parallel control loops. Its modular organization allows to optimize the personalization of cl-DBS therapies to heterogeneous patient profiles. We provide an overview of clinical states and symptoms, as well as putative electrophysiological biomarkers that may be integrated within this structure. This integrative framework may guide future developments and become an integral part of next-generation precision medicine instruments.

Red afterglow and luminescence arising from defects in CaS:Eu2+, Tm3+

CaS:Eu2+, Tm3+ is a phosphor known to emit a long afterglow of red emission (650 nm) when excited by blue light (450 nm). It shows a long afterglow time of 700 s for Eu = 0.05% and Tm = 2%. The mechanism of this afterglow is investigated using time-resolved fluorescence (TR-F) spectroscopy from the nanosecond to millisecond region. At room temperature, it is not possible to investigate shallow levels because of the effects of thermal vibrations. The mechanism of the emission characteristics at room temperature would be affected by these levels that can be observed only at low temperatures. Therefore, the samples are cooled to 15 K for the TR-F measurements. The host material CaS emits blue light (420 nm) arising from sulfur defects, and the typical decay time is measured to be 6 ms. This blue emission becomes stronger when Tm3+ is doped. Furthermore, the doped Eu ions emit a broad red spectrum at 650 nm originating from the Eu2+-specific 4f65d1–4f7 transition. When the excitation is ceased, the red emission decays with a fast time constant of 0.6 μs. This value is a typical decay time for Eu2+. This red emission has multiple decay time constants, and a component with a decay time of 6 ms appears. This 6 ms decay time is the same as that of the blue emission from the sulfur defects, which have an important role on the red afterglow.

Extending the Model-Based Controller Design to Higher-Order Plant Models and Measurement Noise

The article extends a model-based controller design to higher-order systems, focusing on the speed and shapes of the closed loop responses, including the noise attenuation. It shows that, to obtain simple but reliable results, it is necessary to pay attention to the initial process identification and modelling and also to modify the target closed-loop transfer functions, which must remain causal. To attenuate high initial control signal peaks, appropriate pre-filters are introduced. In order to work with as few parameters as possible, all higher-order transfer functions (process models, target closed loops, pre-filters and noise-attenuation filters) are selected in the form of binomial filters with multiple time constants. Consequently, the so-called “half-rule”, used to reduce too complex process transfer functions, has been modified accordingly. Because derived controllers can lead to different transient dynamics depending on the context of use, the article recalls the need to introduce dynamic classes of control to clarify the mission of individual types of controllers. Consequently, also the performance evaluation using the total variation (TV) criterion had to be refined. Indeed, in its original version, TV is not suitable to distinguish between reasonable and excessive control effort due to improper tuning and noise. The modified TVs allow evaluating higher order systems with multiple changes in direction of their control signal increase without contributing to the excessive control increments. The advantages of the proposed modifications, compared to the traditional approaches, are made clear through simulation examples.

Analysis of electrostimulation and electroporation by high repetition rate bursts of nanosecond stimuli

Exposures to short-duration, strong electric field pulses have been utilized for stimulation, ablation, and the delivery of molecules into cells. Ultrashort, nanosecond duration pulses have shown unique benefits, but they require higher field strengths. One way to overcome this requirement is to use trains of nanosecond pulses with high repetition rates, up to the MHz range. Here we present a theoretical model to describe the effects of pulse trains on the plasma membrane and intracellular membranes modeled as resistively charged capacitors. We derive the induced membrane potential and the stimulation threshold as functions of pulse number, pulse duration, and repetition rate. This derivation provides a straightforward method to calculate the membrane charging time constant from experimental data. The derived excitation threshold agrees with nerve stimulation experiments, indicating that nanosecond pulses are not more effective than longer pulses in charging nerve fibers. The derived excitation threshold does not, however, correctly predict the nanosecond stimulation of cardiomyocytes. We show that a better agreement is possible if multiple charging time constants are considered. Finally, we expand the model to intracellular membranes and show that pulse trains do not lead to charge buildup, but can create significant oscillations of the intracellular membrane potential.

Excess Heat Capacity in Mo/Au Transition Edge Sensor Bolometric Detectors.

Excess heat capacity in a bolometric detector has the consequence of increasing or leading to multiple device time constants. The Mo/Au bilayer transition edge sensor (TES) bolometric detectors initially fabricated for the high resolution mid-infrared spectrometer (HIRMES) exhibited two response thermalization scales, one of which is a few times longer than estimates based upon the properties of the bulk materials employed in the design. The relative contribution of this settling time to the overall time response of the detectors is roughly proportional to the pixel area, which ranges between ~0.3 and 2.6 mm2. Use of laser ablation to remove sections of the silicon membranes comprising the pixels results in a detector response with a smaller contribution from the secondary time constant. Additional information about the nature of this excess heat capacity is gleaned from glancing incidence x-ray diffraction, which reveals the presence of molybdenum silicides near the silicon surface which is a consequence of the bi-layer deposition. Quantitative analysis of the concentration of excess molybdenum, estimated with secondary ion mass spectroscopy, is commensurate to the additional heat capacity needed to explain the anomalous time response of the detectors.

Application of EIS to Assess Microbiologically Influenced Steel Corrosion in Marine Fouling Crevice Conditions

Microbiologically influenced corrosion (MIC) can cause severe degradation of civil infrastructure. Recently, severe localized corrosion of steel H-piles submerged in a brackish natural water in a Florida bridge was associated with MIC and fouling (Permeh et al., 2017). The localized corrosion cells/pits were of up to 3" in diameter and penetrated through the steel thickness. Microbiological and chemical analysis of the water samples showed a high population of sulfate reducing bacteria (SRB) and a high concentration of sulfate ions amongst other nutrients. The steel piles had noticeable heavy marine growth which were thought to have an effect on the corrosion process by supporting biofilm development, creating localized corrosion and differential aeration cells (Little et al, 2007). In the work described here electrochemical impedance spectroscopy (EIS) was conducted to characterize the development of biofilm in association with fouling crevice environments.Electrochemical impedance spectroscopy (EIS) has been widely used to assess the electrochemical properties of corrosion systems and has been applied to assess physical biofilm conditions for microbiologically influenced corrosion (MIC) (Mansfeld , 2005). EIS measurements over a wide range of frequencies can be used to identify the electrical characteristics associated with the biofilm and the steel substrate. Both laboratory and field exposure tests were conducted. Field exposure tests included long term exposure (~300 days) of steel coupons at a Florida bridge site that sustained macro- and microfouling organisms. Laboratory tests were conducted in nutrient-rich test solutions inoculated with sulfate reducing bacteria (SRB) in either de-aerated or naturally aerated conditions as well as with idealized crevice geometries. EIS testing was made at the OCP condition with 10 mV AC perturbation voltage from frequencies 100 kHz > f >100 mHz.EIS of the specimens inoculated with SRB and with crevices resulted in impedance responses with multiple loops in the Nyquist diagram. Fitting of the impedance response to equivalent circuit analogs were made to identify biofilm, surface layers, and the steel interfacial characteristics during the experimental exposure (Permeh et al.,2019). For non-crevice specimens without SRB inoculations, the impedance response related to the solution resistance, steel interfacial capacitance and charge transfer resistance, characterized by the Randles circuit. However, for the inoculated specimens, impedance dispersion at high frequencies (sometimes showing a loop in the Nyquist diagram) on first approximation was related to the capacitive and resistive characteristics of the biofilm. In crevice environments, a more complicated behavior arose due to uneven current distribution and heterogeneous impedance within the crevice. The impedance behavior for the porous and laminate crevices can be characterized by multiple time constants associated with the crevice outer material, steel interface, and the current distribution effects in the crevice that can be considered by treatments such as a transmission line. In the inoculated non-crevice specimens, the high frequency impedance dispersion was more readily apparent in the Bode phase angle plot. In that representation, the impedance initially showed a uniform valley with a distinct trough between 10 and 100 mHz. With time, two unique troughs developed at frequencies below 1 Hz (Figure 1) for the inoculated specimens. An increase in capacitance was attributed to biofilm growth.In part to provide a quantitative comparison of the overall impedance of the systems (despite the complicating factors for the crevice specimens), on first approach, the total impedance at 100 mHz (|Z100mHz¬|) was compared. The differences in the total impedance for the various test conditions would reflect the resistive and capacitive electrical behavior of the electrolyte, biofilm, and the steel interface that in turn are directly or indirectly related to SRB activity. EIS identified the development of surface films including by an increase in its capacitive behavior that resulted in lower relative total impedance at a given low frequency (i.e. 100 mHz). Test results confirmed that SRB proliferation and corrosion can occur as the fouling macroorganism can accommodate different environmental condition.

Role of Viscoelasticity in Bacterial Killing by Antimicrobials in Differently Grown Pseudomonas aeruginosa Biofilms.

Pseudomonas aeruginosa colonizes the sputum of most adult cystic fibrosis patients, forming difficult-to-eradicate biofilms in which bacteria are protected in their self-produced extracellular polymeric substance (EPS) matrices. EPS provide biofilms with viscoelastic properties, causing time-dependent relaxation after stress-induced deformation, according to multiple characteristic time constants. These time constants reflect different biofilm (matrix) components. Since the viscoelasticity of biofilms has been related to antimicrobial penetration but not yet bacterial killing, this study aims to relate killing of P. aeruginosa, in its biofilm mode of growth, by three antimicrobials to biofilm viscoelasticity. P. aeruginosa biofilms were grown for 18 h in a constant-depth film fermenter, with mucin-containing artificial sputum medium (ASM+), artificial sputum medium without mucin (ASM-), or Luria-Bertani (LB) broth; this yielded 100-μm-thick biofilms that differed in their amounts of matrix environmental DNA (eDNA) and polysaccharides. Low-load compression testing, followed by three-element Maxwell analyses, showed that the fastest relaxation component, associated with unbound water, was most important in LB-medium-grown biofilms. Slower components due to water with dissolved polysaccharides, insoluble polysaccharides, and eDNA were most important in the relaxation of ASM+-grown biofilms. ASM--grown biofilms showed intermediate stress relaxation. P. aeruginosa in LB-medium-grown biofilms was killed most by exposure to tobramycin, colistin, or an antimicrobial peptide, while ASM+ provided the most protective matrix, with less water and most insoluble polysaccharides and eDNA. In conclusion, stress relaxation of P. aeruginosa biofilms grown in different media revealed differences in matrix composition that, within the constraints of the antimicrobials and growth media applied, correlated with the matrix protection offered against different antimicrobials.

A General Dimension Reduction Method for the Dispersion Modeling of Semiconductor Devices

This paper presents a general dimension reduction method for the dispersion modeling of current and charge sources of semiconductor devices including HEMTs, LDMOS, and HBTs. The dimensions that are easily handled are represented by the existing empirical or physical functions, while those dimensions that are difficult to tackle with or have limited measurement data are represented by the Taylor expansion. In this paper, an AlGaN/GaN HEMT was taken as the example device to illustrate how this method can be applied to handle the comprehensive dispersion effects induced by thermal and charge trapping. The dimensions of terminal voltages ( $V_{\mathit{ gs}}$ , $V_{\mathit{ ds}}$ ) are characterized by the 10-parameter Angelov function, while the remaining dispersion-related dimensions (channel temperature $T_{j}$ and drain trap state $\phi _{D}$ ) are expressed by the Taylor expansion. The constructed drain current source ( $I_{ds}$ ) model is able to predict a number of pulsed $I$ – $V\text{s}$ with various channel temperature and quiescent biases. Finally, the analytical large signal model was implemented in the advanced design system, and several $RC$ sub-circuits with multiple time constants were exploited to implement the dispersion model in the simulator. Good agreement has been achieved for both small-signal and large-signal characteristics of the investigated devices.

Post-glitch exponential relaxation of radio pulsars and magnetars in terms of vortex creep across flux tubes

Timing observations of rapidly rotating neutron stars revealed a great number of glitches, observed both from canonical radio pulsars and magnetars. Among them, 76 glitches have shown exponential relaxation(s) with characteristic decay times ranging from several days to a few months, followed by a more gradual recovery. Glitches displaying exponential relaxation with single or multiple decay time constants are analysed in terms of a model based on the interaction of the vortex lines with the toroidal arrangement of flux tubes in the outer core of the neutron star. Model results agree with the observed timescales in general. Thus, the glitch phenomenon can be used to deduce valuable information about neutron star structure, in particular on the interior magnetic field configuration which is unaccessible from surface observations. One immediate conclusion is that the magnetar glitch data are best explained with a much cooler core and therefore require that direct Urca type fast cooling mechanisms should be effective for magnetars.

Multi-timescale Parametric Electrical Battery Model for Use in Dynamic Electric Vehicle Simulations

Simulation of electric vehicles (EVs) over driving schedules within a fully dynamic EV simulator requires battery models capable of accurately and quickly predicting state of charge (SOC), $I$ – $V$ characteristics, and dynamic behavior of various battery types. An electric battery model utilizing multiple time constants, to address ranges of seconds, minutes, and hours, is developed. The model parameters include open-circuit voltage, series resistance, and equivalent RC circuits, with nonlinear dependence on battery SOC. The SOC captures effects from discharge and charge rate, temperature, and battery cycling. Thermal modeling predicting real-time battery temperature is introduced. One focus of this paper is presenting a systematic and generic methodology for parameter extraction as well as obtaining SOC factors through reasonable test work when evaluating any given lithium-ion (Li-ion), nickel-metal hydride, or lead-acid battery cell. In particular, data sets for a Panasonic CGR18650 Li-ion battery cell are tabulated for direct use. The Li-ion battery model is programmed into a MATLAB/Simulink environment and used as a power source within an existing comprehensive dynamic vehicle simulator. Validation of the Simulink model is through a battery testing apparatus with a hardware-in-the-loop driving schedule that cycles real batteries. Results from simulations and measurements of Li-ion battery packs show that the proposed battery model behaves well and interacts appropriately with other subcomponents of the vehicle simulator.

New Insights into the State Trapping of UV-Excited Thymine.

After UV excitation, gas phase thymine returns to a ground state in 5 to 7 ps, showing multiple time constants. There is no consensus on the assignment of these processes, with a dispute between models claiming that thymine is trapped either in the first (S1) or in the second (S2) excited states. In the present study, a nonadiabatic dynamics simulation of thymine is performed on the basis of ADC(2) surfaces, to understand the role of dynamic electron correlation on the deactivation pathways. The results show that trapping in S2 is strongly reduced in comparison to previous simulations considering only non-dynamic electron correlation on CASSCF surfaces. The reason for the difference is traced back to the energetic cost for formation of a CO π bond in S2.

Ultrafast Two-Electron Transfer in a CdS Quantum Dot-Extended-Viologen Cyclophane Complex.

Time-resolved optical spectroscopies reveal multielectron transfer from the biexcitonic state of a CdS quantum dot to an adsorbed tetracationic compound cyclobis(4,4'-(1,4-phenylene) bipyridin-1-ium-1,4-phenylene-bis(methylene)) (ExBox(4+)) to form both the ExBox(3+•) and the doubly reduced ExBox(2(+•)) states from a single laser pulse. Electron transfer in the single-exciton regime occurs in 1 ps. At higher excitation powers the second electron transfer takes ∼5 ps, which leads to a mixture of redox states of the acceptor ligand. The doubly reduced ExBox(2(+•)) state has a lifetime of ∼10 ns, while CdS(+•):ExBox(3+•) recombines with multiple time constants, the longest of which is ∼300 μs. The long-lived charge separation and ability to accumulate multiple charges on ExBox(4+) demonstrate the potential of the CdS:ExBox(4+) complex to serve as a platform for two-electron photocatalysis.

Surface flood and underground flood in Xiangxi River Karst Basin: Characteristics, models, and comparisons

Xiangxi River Basin, located in western Hubei Province in central China, is a karst ridge-trough area with an inhomogeneous and complicated distribution of water resources. This paper compares the characteristics of surface and subsurface floods in this karst basin, utilizing a one-parameter Darcian model and the traditional exponential model. The observed hydrographs and inferred water components are strikingly similar for surface and subsurface floods. The Darcian model and the exponential model are based on different views of the flood generation process, with the former fitting the entire hydrograph with a single time constant, and the latter fitting only the recession limb with multiple time constants. Due to the anisotropy and heterogeneity of karst media, a combination of physical and chemical techniques including the use of 3S (remote sensing, geographical information system, global positioning system) method is proposed for an enhanced hydrological investigation to assess and characterize karst water resources in mountainous areas.

Investigating the Solid Electrolyte Interphase Formed by Additive Reduction Using Physics-Based Modeling

In lithium-ion batteries, chemical additives are used as co-solvents to primary electrolytes to improve capacity and power retention. These additives facilitate the formation of a passivation layer, the solid electrolyte interphase (SEI), on the electrode surface. In this work, SEIs are formed in neat electrolyte and in electrolyte containing fluoroethylene carbonate and vinylene carbonate. The formed SEIs are then compared using a redox couple to probe their physical properties. For passivated samples, the impedance response of the redox couple shows the presence of multiple time constants, with processes at longer time scales corresponding to redox couple transport in the porous layer of the SEI. Samples passivated with additive-containing electrolyte versus neat electrolyte exhibit less redox-couple kinetic and mass-transport impedance. Simulations of the electrode-electrolyte interface indicate that compact and porous layer growth lead to slowed redox kinetics and mass transport. Model results suggest that SEI thicknesses are found to be at least an order of magnitude larger than expected compared to graphite electrodes. SEM cross sections of SEIs formed by neat and additive-containing electrolyte support the model findings. Experimentally measured formation charges, coupled with FTIR measurements of SEI composition, suggest that polymerization reactions are causing the unexpected film growth.