Impact Of Non-idealities Research Articles

Reliability assessment and electromagnetic controller for semi-active impact damper in structural vibration control

This study proposes a semi-active controller for impact dampers to address the challenge of achieving ideal impacts that occur exclusively when the structure reaches to its equilibrium position. The control effectiveness and reliability of the semi-active impact damper (SAID) both over time and with parameter variations are assessed and compared with passive impact dampers. Furthermore, the performance of SAID under deviations from the ideal control strategy is investigated, considering three types of non-ideal impact time and friction effects. The mathematical solution for the ideal control strategy is derived, and a strong positive correlation is found between control efficiency and SAID parameters through theoretical analysis and numerical simulation. The corresponding suggestions are provided for addressing parameter variations and deviations from ideal control strategy of SAID. Based on the investigation of extended impact conditions, a feasible SAID controller configuration with adjustable gap clearance is proposed, effectively addressing time lag issues. Experimental results validate the numerical method and practical implementation of the proposed electromagnetic controller for SAID, which can efficiently control structural responses under random low-frequency excitations such as earthquakes.

Impact of Non-Idealities on the Behavior of Probabilistic Computing: Theoretical Investigation and Analysis

Impact of Non-Idealities on the Behavior of Probabilistic Computing: Theoretical Investigation and Analysis

Estimating evaporation rates and contaminant air concentrations due to small spills of non-ideal aqueous organic solvent mixtures in a controlled environment

Although small spills of non-ideal organic solvent mixtures are ubiquitous undesirable events in occupational settings, the potential risk of exposure associated with such scenarios remains insufficiently investigated. This study aimed to examine the impact of non-ideality on evaporation rates and contaminant air concentrations resulting from small spills of organic solvent mixtures. Evaporation rate constants alphas (α) were experimentally measured for five pure solvents using a gravimetric approach during solvent evaporation tests designed to simulate small spills of solvents. Two equations were used for estimating contaminants’ evaporation rates from aqueous mixtures assuming either ideal or non-ideal behavior based on the pure-chemical alpha values. A spill model also known as the well-mixed room model with exponentially decreasing emission rate was used to predict air concentrations during various spill scenarios based on the two sets of estimated evaporation rates. Model predictive performance was evaluated by comparing the estimates against real-time concentrations measured for the same scenarios. Evaluations for 12 binary non-ideal aqueous mixtures found that the estimated evaporation rates accounting for the correction by the activity coefficients of the solvents (median = 0.0318 min−1) were higher than the evaporation rates estimated without the correction factor (median = 0.00632 min−1). Model estimates using the corrected evaporation rates reasonably agreed with the measured values, with a median predicted peak concentrations-to-measured peak concentrations ratio of 0.92 (0.81 to 1.32) and a median difference between the predicted and the measured peak times of −5 min. By contrast, when the non-corrected evaporation rates were used, the median predicted peak concentrations-to-measured peak concentrations ratio was 0.31 (0.08 to 0.75) and the median difference between the predicted and the measured peak times was +33 min. Results from this study demonstrate the importance of considering the non-ideality effect for accurately estimating evaporation rates and contaminant air concentrations generated by solvent mixtures. Moreover, this study is a step further in improving knowledge of modeling exposures related to small spills of organic solvent mixtures.

Design Considerations for 2-D Dirac-Source FETs—Part II: Nonidealities and Benchmarking

In Part I of this article, we discussed the basic operation of 2-D Dirac-source field-effect transistors (DS-FETs) and studied the impact of key device parameters on the device performance. In this article, we continue to study the impact of nonidealities on the performance of DS-FETs, such as graphene disorder and rethermalization, as well as ways to mitigate them. In addition, we study the performance improvement by introducing a bandgap in the graphene source. Finally, we benchmark the performance of DS-FETs for different channel materials, providing a guide for the proper choice of material for 2-D DS-FETs.

Design Considerations for 2-D Dirac-Source FETs—Part I: Basic Operation and Device Parameters

Dirac-source field-effect transistors (DS-FETs) have been proposed as promising candidates for low-power switching devices by leveraging the Dirac cone of graphene as a low-pass energy filter. In particular, using 2-D materials as the channel in a DS-FET is of interest for ultimate scaling purposes. In this article, we investigate the design considerations for 2-D DS-FETs using ballistic simulations based on the Landauer formalism. We study the impact of several key device parameters on the device performance, such as graphene doping, Schottky barrier heights, and effective mass of the 2-D channel. In Part II of this article, we study the impact of nonidealities on the performance of DS-FETs and benchmark the performance of DS-FETs for different channel materials.

Impact of non-ideality on reconstructing spatial and temporal variations in aerosol acidity with multiphase buffer theory

Abstract. Aerosol acidity is a key parameter in atmospheric aqueous chemistry and strongly influences the interactions of air pollutants and the ecosystem. The recently proposed multiphase buffer theory provides a framework to reconstruct long-term trends and spatial variations in aerosol pH based on the effective acid dissociation constant of ammonia (Ka,NH3∗). However, non-ideality in aerosol droplets is a major challenge limiting its broad applications. Here, we introduced a non-ideality correction factor (cni) and investigated its governing factors. We found that besides relative humidity (RH) and temperature, cni is mainly determined by the molar fraction of NO3- in aqueous-phase anions, due to different NH4+ activity coefficients between (NH4)2SO4- and NH4NO3-dominated aerosols. A parameterization method is thus proposed to estimate cni at a given RH, temperature and NO3- fraction, and it is validated against long-term observations and global simulations. In the ammonia-buffered regime, with cni correction, the buffer theory can reproduce well the Ka,NH3∗ predicted by comprehensive thermodynamic models, with a root-mean-square deviation ∼ 0.1 and a correlation coefficient ∼ 1. Note that, while cni is needed to predict Ka,NH3∗ levels, it is usually not the dominant contributor to its variations, as ∼ 90 % of the temporal or spatial variations in Ka,NH3∗ are due to variations in aerosol water and temperature.

TxSim: Modeling Training of Deep Neural Networks on Resistive Crossbar Systems

Deep neural networks (DNNs) have gained tremendous popularity in recent years due to their ability to achieve superhuman accuracy in a wide variety of machine learning tasks. However, the compute and memory requirements of DNNs have grown rapidly, creating a need for energy-efficient hardware. Resistive crossbars have attracted significant interest in the design of the next generation of DNN accelerators due to their ability to natively execute massively parallel vector-matrix multiplications within dense memory arrays. However, crossbar-based computations face a major challenge due to device and circuit-level nonidealities, which manifest as errors in the vector-matrix multiplications and eventually degrade DNN accuracy. To address this challenge, there is a need for tools that can model the functional impact of nonidealities on DNN training and inference. Existing efforts toward this goal are either limited to inference or are too slow to be used for large-scale DNN training. We propose TxSim, a fast and customizable modeling framework to functionally evaluate DNN training on crossbar-based hardware considering the impact of nonidealities. The key features of TxSim that differentiate it from prior efforts are: 1) it comprehensively models nonidealities during all training operations (forward propagation, backward propagation, and weight update) and 2) it achieves computational efficiency by mapping crossbar evaluations to well-optimized Basic Linear Algebra Subprograms (BLAS) routines and incorporates speedup techniques to further reduce simulation time with minimal impact on accuracy. TxSim achieves 6×- 108× improvement in simulation speed over prior works, and thereby makes it feasible to evaluate the training of large-scale DNNs on crossbars. Our experiments using TxSim reveal that the accuracy degradation in DNN training due to nonidealities can be substantial (3%-36.4%) for large-scale DNNs and data sets, underscoring the need for further research in mitigation techniques. We also analyze the impact of various device and circuit-level parameters and the associated nonidealities to provide key insights that can guide the design of crossbar-based DNN training accelerators.

Four quadrant analog multiplier based memristor emulator using single active element

This paper presents a novel Four Quadrant Analog Multiplier (FQAM) circuit and its applications using a single active element Current Differencing Transconductance Amplifier (CDTA) and two NMOS. This circuit has a cascadability feature as it produces current and voltage outputs at high and low impedance ports, respectively. It offers additional features such as resistor-less realization, operability in voltage and trans-conductance mode, and configurable structure. Further, the FQAM circuit is configured to develop a memristor emulator based on the proposed mathematical analogy. The proposed memristor circuit contains active elements (one CDTA, two NMOS, and one Inverting Voltage buffer) and only one grounded capacitor. It offers tunability using the transconductance gain of the CDTA block. Also, the proposed memristor emulator circuit doesn’t contain any additional multiplier block. The emulator circuit can be operated in both the Incremental and the Decremental mode of memristance variation. The results demonstrate the non-volatile property as well as hysteresis behavior for the wide frequency range. The effects of statistical variation in passive component, threshold voltage, and aspect ratios on the proposed circuits using Monte-Carlo simulation have been estimated. Also, the impact of non-idealities and the parasitic effects of the CDTA on the proposed circuits are investigated. In last, the capacitor-less version of the memristor emulator and its hysteresis characteristics have been demonstrated. The simulation results obtained using HSPICE, are agreed well with the theoretical analysis.

Treatment of non-ideality in the SPACCIM multiphase model – Part 2: Impacts on the multiphase chemical processing in deliquesced aerosol particles

Abstract. Tropospheric deliquesced particles are characterised by concentrated non-ideal solutions (“aerosol liquid water” or ALW) that can affect the occurring multiphase chemistry. However, such non-ideal solution effects have generally not yet been considered in and investigated by current complex multiphase chemistry models in an adequate way. Therefore, the present study aims at accessing the impact of non-ideality on multiphase chemical processing in concentrated aqueous aerosols. Simulations with the multiphase chemistry model (SPACCIM-SpactMod) are performed under different environmental and microphysical conditions with and without a treatment of non-ideal solutions in order to assess its impact on aqueous-phase chemical processing. The present study shows that activity coefficients of inorganic ions are often below unity under 90 % RH-deliquesced aerosol conditions and that most uncharged organic compounds exhibit activity coefficient values of around or even above unity. Due to this behaviour, model studies have revealed that the inclusion of non-ideality considerably affects the multiphase chemical processing of transition metal ions (TMIs), oxidants, and related chemical subsystems such as organic chemistry. In detail, both the chemical formation and oxidation rates of Fe(II) are substantially lowered by a factor of 2.8 in the non-ideal base case compared to the ideal case. The reduced Fe(II) processing in the non-ideal base case, including lowered chemical rates of the Fenton reaction (−70 %), leads to a reduced processing of HOx∕HOy under deliquesced aerosol conditions. Consequently, higher multiphase H2O2 concentrations (larger by a factor of 3.1) and lower aqueous-phase OH concentrations (lower by a factor of ≈4) are modelled during non-cloud periods. For H2O2, a comparison of the chemical reaction rates reveals that the most important sink, the reaction with HSO3-, contributes with a 40 % higher rate in the non-ideal base case than in the ideal case, leading to more efficient sulfate formation. On the other hand, the chemical formation rates of the OH radical are about 50 % lower in the non-ideal base case than in the ideal case, leading to lower degradation rates of organic aerosol components. Thus, considering non-ideality influences the chemical processing and the concentrations of organic compounds under deliquesced particle conditions in a compound-specific manner. For example, the reduced oxidation budget under deliquesced particle conditions leads to both increased and decreased concentration levels, e.g. of important C2∕C3 carboxylic acids. For oxalic acid, the present study demonstrates that the non-ideality treatment enables more realistic predictions of high oxalate concentrations than observed under ambient highly polluted conditions. Furthermore, the simulations imply that lower humidity conditions, i.e. more concentrated solutions, might promote higher oxalic acid concentration levels in aqueous aerosols due to differently affected formation and degradation processes.

The impact of non-ideality of lipid mixing on peptide induced lipid clustering

The influence of several antimicrobial trivalent cyclic hexapeptides on the mixing behavior of bilayer lipid membranes containing phosphatidylglycerol (PG) and phosphatidylethanolamine (PE) with varying composition was studied using DSC and ITC. The peptides contained three arginines and three aromatic amino acids and had different sequences. All of them induce clustering of PG-rich clusters with bound peptides after binding. In a previous publication we could show that a correlation between clustering efficacy and the antimicrobial activity of the peptides exists (S. Finger et al., Biochim. Biophys. Acta 1848 (2015) 2998–3006). In the current study we investigated whether the non-ideality of the lipid mixture had any effect on the clustering efficacy and the critical peptide/lipid clustering ratio. We could show that for PG/PE membranes containing 1:1 M ratios and lipids with equal or unequal chain lengths, the amount of clustered PG depended only slightly on the absolute chain length and on the chain length difference between PG and PE. Much larger differences were observed when the PG/ PE mixing ratio was changed. In mixtures of DPPG/DPPE with high PG content, the amount of clustered PG per added peptide was much higher than in PE-rich mixtures. The ITC experiments showed that the critical peptide/lipid ratio for cluster formation is also strongly dependent on the PG/PE ratio in the mixture. In the PG/PE 3:1 mixture, the formation of clusters with bound peptide is much more likely than for mixtures with less PG. For 1:1 and 1:3 lipid mixtures, the critical peptide/lipid ratio for demixing is between 0.002 and 0.004. Therefore, even in these mixtures clustering occurs way below charge saturation of the PG in the mixture and the PG-rich clusters are not charge compensated either. The peptide concentration necessary for inducing clustering amounts to ~8 μM, a value well within the range of minimal inhibitory concentration values observed for the cyclic peptides studied here. Our results show that not only the structure of the cyclic peptide influences the clustering efficacy but also the mixing behavior of the lipids in the bilayers has an influence on the amount of clustering induced by binding of cyclic peptides.

A Two-Stage Switched-Capacitor Integrator for High Gain Inverter-Like Architectures

A discrete-time, switched capacitor integrator is presented. The integrator is based on a two-stage architecture where the first stage converts the input voltage into a charge that is accumulated into the second stage. The main strength of the proposed circuit is a higher dc gain with respect to previous solutions, making it optimal for low-voltage inverter-like integrators. A further advantage is the fact that, in contrast with existing solutions, the output voltage is valid across the whole clock cycle. Theoretical analysis of the circuit is performed to calculate the dependence of the integrator dc gain and input-referred offset voltage on the corresponding parameters of the constituting amplifiers. Discrete-time simulations are performed to estimate the gain and phase error with respect to an ideal integrator. The results of electrical simulations performed on an inverter-like prototype, designed with the UMC 0.18- ${\mu }\text{m}$ CMOS process, are presented to show the impact of non-idealities from the amplifiers and switches.

Low‐power non‐ideal pulse‐width modulated DC–DC buck–boost converter: design, analysis and experimentation

In this study, parasitic elements (non-idealities) effect on a low-power DC-DC buck-boost converter design is analysed and investigation is carried out by both large (i.e. steady-state) and small signal analysis. The large signal analysis of non-ideal buck-boost converter explored the significant information such as nearly accurate duty cycle, maximum allowable duty cycle and maximum possible output voltage. Further, accurate mathematical design formulae are derived of inductor and capacitor for specified inductor current ripple and output voltage ripple (OVR), respectively. Moreover, consequences of different equivalent series resistance of capacitor on OVR is examined. Subsequently, the exact model of buck-boost converter is procured from the small signal analysis, which is almost analogous to practical system. In order to show the impact of non-idealities on controller design, an internal model control PID controller is designed for ideal, semi-non-ideal and complete non-ideal systems based on their respective models, which shows the controller based on non-ideal model provides very close results to practical system. Conclusively, the complete theoretical explorations are justified by simulations and substantiated by experimental results.

The Role of Nonidealities in the Scaling of MoS2 FETs

2-D material FETs hold the promise of excellent gate control, but the impact of nonidealities on their performance remains poorly understood. This is because of the need, so far, to use computationally intensive nonequilibrium Green’s function (NEGF) simulations. Here, we therefore use a semiclassical model to investigate the role of nonidealities in the scaling of back-gated (BG) and top-gated (TG) monolayer MoS2 FETs. We verify the electrostatics and transport of the semiclassical model with density functional theory-based NEGF simulations and calibrate nonidealities, such as interface traps ( ${D}_{\textsf {it}}$ ) and Schottky contact barrier height ( $\phi _{\textsf {SB}}$ ) to experimental monolayer and bilayer MoS2 FETs. We find that among the nonidealities, ${D}_{\textsf {it}}$ has the strongest subthreshold swing impact with 70 mV/dec obtainable in BG devices for a ${D}_{\textsf {it}}$ of $5\times {10}^{11}$ cm−2eV $^{-1}$ , an equivalent oxide thickness (EOT) of 1 nm, and a channel length ( ${L}_{\textsf {ch}}$ ) of 5 nm. For scaled EOT, $\phi _{\textsf {SB}}$ only strongly impacts ${I}_{ \mathrm{\scriptscriptstyle ON}}$ for the TG case, as the overlapping gate thins the Schottky barriers in the BG case. We show in TG devices that a spacer of only 5 nm results in a 1000-fold drop in ${I}_{ \mathrm{\scriptscriptstyle ON}}$ because of the nonidealities. We propose positive spacer oxide charge as a solution and show that a charge density of above 1013 cm−2 is required to fully recover the device performance.

Modeling Edge Recombination in Silicon Solar Cells

A new approach to model edge recombination in silicon solar cells is presented. The model accounts for recombination both at the edge of the quasi-neutral bulk as well as at an exposed space-charge-region (SCR), the latter via an edge-length-specific diode property with an ideality factor of 2: a localized J02, edge. The model is implemented in Quokka3, where the $J_{02,edge}$ is applied locally to the edges of the three-dimensional geometry, imposing less simplifying assumptions compared with the common way of applying it as an external diode. A “worst-case” value for $J_{02,{\rm{edge}}}$ , assuming very high surface recombination, is determined by fitting to full detailed device simulations which resolve the SCR recombination. A value of $\sim \text{19 nA/cm}$ is found, which is shown to be largely independent of device properties. The new approach is applied to model the impact of edge recombination on full cell performance for a substantial variety of device properties. It is found that recombination at the quasi-neutral bulk edge does not increase the $J_{02}$ of the dark J–V curve, but still shows a nonideal impact on the light J–V curve similar to the SCR recombination. This needs to be considered in the experimental evaluation of edge losses, which is commonly performed via fitting $J_{02}$ to dark J–V curves.

Impact of Non-idealities on the Performance of InAs/(In)GaAsSb/GaSb Tunnel FETs

Measured InGaAsSb/InAs nanowire TFETs showing both, sub-60mV/dec slope and high ON-current, are simulated using calibrated TCAD. The focus is laid on the impact of non-idealities, such as hetero-interface traps, oxide-interface traps, and bulk traps on device characteristics. Simulated temperature-dependent transfer curves are in good agreement with the measured data which validates the simulation set-up. It is found that trap-assisted tunneling involving bulk traps adjacent to the hetero-junction is primarily responsible for the degradation of the swing. Due to the small diameter of the nanowire, trap-assisted tunneling is inhibited at the InAs/oxide interface. Still, oxide interface traps reduce the electrostatic coupling between gate and channel, which further increases the swing. The TCAD analysis correctly predicts the negative transconductance observed at high gate bias. If the same simulation set-up is used to study the effect of gate alignment, a significant improvement of both ON-current and swing is found.

Analysis of Photonics-Based RF Beamforming With Large Instantaneous Bandwidth

Since the photonics-based true time delay could significantly broaden the instantaneous bandwidth of a phased antenna array system, solutions utilizing wideband signals could be enabled to considerably enhance the functionality and performance of RF systems. To investigate the features of the wideband beamforming, a comprehensive theoretical model is developed in this paper to analyze the photonics-based broadband beamforming network for uniform linear arrays. In the proposed model, the performance of the beamforming network over the operational frequency band is intuitively depicted through a two-dimensional spatial-temporal frequency response, in which both the spatial frequency (or the corresponding observation angle) and the temporal frequency are adopted as independent variables. In addition, cross correlation of the original signal and the signal that undergoes the beamforming network is calculated to define a wideband pattern and a new figure of merit, so that the waveform-dependent overall response over a large bandwidth can be evaluated. Based on the theoretical model, a time-domain method for pattern measurement is proposed and experimentally demonstrated, which offers the coincident result as the frequency-domain method but is more convenient to be conducted. Numerical results of several typical photonics-based beamforming structures are presented to investigate the impact of nonidealities on the two-dimensional response and the proposed figure of merit.

Transient Radar Method: Novel Illumination and Blind Electromagnetic/Geometrical Parameter Extraction Technique for Multilayer Structures

A novel technique enabling ultrafast nondestructive characterization of multilayer dielectric structures is proposed. Actual estimations indicate that the data acquisition performance of electronic measurement systems of today allow deep submillimeter depth resolution, almost independently of the frequency. For a 10 GHz signal, e.g., this corresponds to significant subwavelength depth resolution. By means of a novel blind analysis method of the time-dependent reflected electromagnetic (EM) signal, detailed information on the geometrical and EM parameters such as the complex valued dielectric permittivity and magnetic susceptibility of each layer of the structure can be extracted. We validate the novel technique for different materials in the 10 GHz range and compare the results obtained with S-parameter measurements in the 9.5–10.5 GHz range using a vector network analyzer. We will discuss the impact of nonidealities on the accuracy of the retrieved parameters. The novel technique has the potential for deployment in a wide range of applications ranging from the piping industry, wind energy industry, automotive, biotechnology, food industry, pharmacy, and so on.

Analysis and Design of VCO-Based Phase-Domain $\Sigma \Delta $ Modulators

VCO-based phase-domain $\Sigma \Delta $ modulators employ the combination of a voltage-controlled-oscillator (VCO) and an up/down counter to replace the analog loop filter used in conventional $\Sigma \Delta $ modulators. Thanks to this highly digital architecture, they can be quite compact, and are expected to shrink even further with CMOS scaling. This paper describes the analysis and design of such converters. Trade-offs between design parameters and the impact of non-idealities, such as finite counter length and VCO non-linearity, are assessed through both theoretical analysis and behavioral simulations. The proposed design methodology is applied to the design of a phase-to-digital converter in a 40-nm CMOS process, which is used to digitize the output of a thermal-diffusivity temperature sensor, achieving ± 0.2° ( $3\sigma $ ) phase inaccuracy from -40 to 125 °C and a sensor-limited resolution of 57 m° (RMS) within a 500-Hz bandwidth. Measurements on the prototype agree quite well with theoretical predictions, thus demonstrating the validity of the proposed design methodology.

Localization in finite vibroimpact chains: Discrete breathers and multibreathers.

We explore the dynamics of strongly localized periodic solutions (discrete solitons or discrete breathers) in a finite one-dimensional chain of oscillators. Localization patterns with both single and multiple localization sites (breathers and multibreathers) are considered. The model involves parabolic on-site potential with rigid constraints (the displacement domain of each particle is finite) and a linear nearest-neighbor coupling. When the particle approaches the constraint, it undergoes an inelastic impact according to Newton's impact model. The rigid nonideal impact constraints are the only source of nonlinearity and damping in the system. We demonstrate that this vibro-impact model allows derivation of exact analytic solutions for the breathers and multibreathers with an arbitrary set of localization sites, both in conservative and in forced-damped settings. Periodic boundary conditions are considered; exact solutions for other types of boundary conditions are also available. Local character of the nonlinearity permits explicit derivation of a monodromy matrix for the breather solutions. Consequently, the stability of the derived breather and multibreather solutions can be efficiently studied in the framework of simple methods of linear algebra, and with rather moderate computational efforts. One reveals that that the finiteness of the chain fragment and possible proximity of the localization sites strongly affect both the existence and the stability patterns of these localized solutions.

Impact of non-idealities in gas-tracer tests on the estimation of reaeration, respiration, and photosynthesis rates in streams

Estimating respiration and photosynthesis rates in streams usually requires good knowledge of reaeration at the given locations. For this purpose, gas-tracer tests can be conducted, and reaeration rate coefficients are determined from the decrease in gas concentration along the river stretch. The typical procedure for analysis of such tests is based on simplifying assumptions, as it neglects dispersion altogether and does not consider possible fluctuations and trends in the input signal. We mathematically derive the influence of these non-idealities on estimated reaeration rates and how they are propagated onto the evaluation of aerobic respiration and photosynthesis rates from oxygen monitoring. We apply the approach to field data obtained from a gas-tracer test using propane in a second-order stream in Southwest Germany. We calculate the reaeration rate coefficients accounting for dispersion as well as trends and uncertainty in the input signals and compare them to the standard approach. We show that neglecting dispersion significantly underestimates reaeration, and results between sections cannot be compared if trends in the input signal of the gas tracer are disregarded. Using time series of dissolved oxygen and the various estimates of reaeration, we infer respiration and photosynthesis rates for the same stream section, demonstrating that the bias and uncertainty of reaeration using the different approaches significantly affects the calculation of metabolic rates.