Nonlinear Threshold Research Articles

Optical damage and the third-order nonlinearity in GeGaS glasses

We have measured optical properties of GexGa4S96-x (x=22.5, 27, 30, 33.3 and 36) glasses including optical bandgap Eg, hardness, linear and nonlinear refractive index and laser damage threshold. We found that, both Eg and laser damage threshold exhibit maximum values in Ge30Ga4S66 glass, linear refractive index increases with increasing Ge content, but nonlinear refractive index has a minimum in Ge30Ga4S66, and their correlation can be well described by the Miller’s rule. We conclude that, Ge30Ga4S66 glass with chemically stoichiometric composition might be ideal for the chalcogenide-based optical amplifiers since it has reasonable optical nonlinearity, and high figure of merit (FOM) and laser damage threshold.

Characteristic of fixed abrasive polishing for KDP in an anhydrous environment.

High grade optical components are rapidly being employed in a wide range of applications due to their great performance. Among these, KDP (potassium dihydrogen phosphate) is the preferred choice for frequency doubling components because to its large non-linear optical technique and high laser damage threshold. In this research, KDP is treated employing fixed polishing in an anhydrous environment. Copper oxide is utilized as abrasive, and toner and phenolic resin are combined to form pellets for KDP polishing. Calculation of the temperature field on the surface of the workpiece based on the relationship of the movement. The ideal polishing parameters are also determined from the findings of the temperature field and the optimum process parameters are 5kPa pressure, 150rpm and 8mm eccentricity. A new material removal model is presented and based on this, a unique processing technique to increase the material removal depth is provided. Interestingly, with this form of polishing, the surface roughness of the workpiece remains about Ra 20nm after a quick shift and does not alter with re-pressing.

Natural convection in a fluid saturating an anisotropic porous medium in LTNE: effect of depth-dependent viscosity

Thermal convection in a fluid saturating an anisotropic porous medium in local thermal nonequilibrium (LTNE) is investigated, with specific attention to the effect of variable viscosity on the onset of convection. Many fluids show a remarkable dependence of viscosity on temperature that cannot be neglected. For this reason, we take into account a fluid whose viscosity decreases exponentially with depth, according to Straughan (Acta Mech. 61:59–72, 1986), Torrance and Turcotte (J. Fluid Mech. 47(1):113–125, 1971). The novelty of this paper is to highlight how variable viscosity coupled with the LTNE assumption affects the onset of convection. A numerical procedure shows the destabilising effect of depth-dependent viscosity. Moreover, it comes out that the LTNE hypothesis makes the influence of viscosity more intense. Linear instability analysis of the conduction solution is carried out by means of the Chebyshev-tau method coupled to the QZ algorithm, which provides the critical Rayleigh number for the onset of convection in a straightforward way. The energy method is employed in order to study the nonlinear stability. The optimal result of coincidence between the linear instability threshold and the global nonlinear stability threshold is obtained. The influence of anisotropic permeability and conductivity, weighted conductivity ratio, and interaction coefficient on the onset of convection is highlighted.

A sliding-window based signal processing method for characterizing particle clusters in gas-solids high-density CFB reactor

Particle clusters in CFB risers were identified from the instantaneous solids holdup signals by a new sliding-window based signal processing method. By shifting the time window and calculating the mean and the standard deviation within it, a non-linear threshold curve for identifying the clusters was derived instead of the conventional constant threshold. The optimal sliding window size was determined as Wb = 1024 data points by the bisection method on the entire piece of signals. Using the proposed method, a more realistic characterization of the particle clusters in both HDCFB and LDCFB was obtained by considering the bulk fluctuation of the gas-solids flow. The clusters in HDCFB have higher solids holdup and lower velocity than that in the LDCFB. The HDCFB is also found to have a greater number of loose clusters for better gas-solids contacting and exchanges in the center of the riser.

Nonlinear threshold approach for asymmetric effects of government size on economic growth in an emerging Asian economy: the Malaysian experience

This paper discovers the asymmetric relation between government size and economic growth in Malaysia, an emerging Asian economy, by utilising a dynamic threshold nonlinear approach. The study finds empiric evidence that the threshold effect linking government size to economic growth in Malaysia exists when two different proxies of government size are set as the threshold variable. On closer inspection, it is found that an inverted U-shaped Armey curve is present when allowing for endogenous government size threshold proxied by government operating/real GDP. However, a U-shaped curve of nonlinear relationship exists instead when the government investment/real GDP serves as the threshold variable. In general, this paper gives policymakers a real insight into the optimal government size in Malaysia especially when designing an effectual fiscal policy to advance sustainable economic growth to materialise its Shared Prosperity Vision by the year 2030.

Origins of THz Modes and Their IR Intensities in LiNbO3

LiNbO3 crystals have been essential materials for generating freely propagating terahertz (THz) pulses among other materials because of their excellent nonlinear optical properties and high damage thresholds. However, one of their dielectric properties─the huge IR intensities of THz modes─has been impeding their practical applications. Such IR intensities produce additional contributions to the refractive index, making the phase-matching between the optical pump and THz radiation difficult. The large IR intensities also lead to strong THz absorptions, reducing the conversion coefficient. Although a couple of techniques have been applied to solve or avoid the relevant problems, a more fundamental question regarding the atomic mechanism of generating the huge IR intensities of THz modes in LiNbO3 has not been discussed so far. We performed a rigorous analysis of the nature of THz modes in terms of the contributions from the constituent atoms Li, Nb, and O using a quantitative approach originally developed in the previous studies. We further clarified the roles played by the motions of the constituent atoms in generating IR intensities by calculating the associated Born charge vectors. We revealed that the librations of the O octahedra, despite their prominent presence in some THz modes, are IR-silent motions. The translations of the O octahedra and Nb cations are the leading contributors to IR intensities, while the internal vibrations of the O octahedra play a destructive role. We propose two mechanisms for reducing the IR intensities of THz modes in LiNbO3 based on the analyzed results.

Global dynamics of a Filippov epidemic system with nonlinear thresholds

Due to the intermittency of prevention and control measures, the right-hand function of the dynamic model describing the spread of infectious disease is often induced to be nonsmooth, which can be formulated by employing Filippov systems and have been widely studied recently. Note that these systems only consider the number of infected individuals as the switching threshold. However, infectious disease control depends not only on the number of infected individuals, but also on the change rate of infected individuals. To address this, we propose a Filippov system with media-influenced nonlinear thresholds which integrate the change rate of infected individuals into the threshold strategy. The main results reveal that the proposed threshold strategy can induce the complex dynamic behavior, including multiple sliding segments and pseudo-equilibrium. Furthermore, our main results show that variations of threshold (ET) and the nonlinear threshold control strategy not only lead to rich dynamics including bistability, but also have important implications for disease control.

Strategies to Control the Relaxation Kinetics of Ag‐Based Diffusive Memristors and Implications for Device Operation

AbstractDiffusive memristors based on volatile electrochemical metallization (v‐ECM) devices are of broad interest for applications in emerging memory technologies and neuromorphic computing areas due to their interesting features such as thresholding, self‐relaxation, and energy‐efficient switching behaviors. Recently, the nonlinear threshold kinetics and the correlation of filament formation and growth with its relaxation behavior are uncovered from a physical perspective. However, the complexity of the diffusive memristors’ behavior might still hamper a straight transfer into emerging computing applications. Facing this challenge means going beyond the single device level and understanding the impact of other circuitry elements for further optimization of device operation. In this work, the effect of a series resistor on the switching dynamics of Ag/HfO2/Pt diffusive memristor devices by deploying various programming schemes with different resistances is investigated. Furthermore, all results and their implications on devices’ operation are compressively discussed. These findings help to further advance the optimization of the operating condition of diffusive memristors.

Association between triglyceride-to-high density lipoprotein cholesterol ratio and three-month outcome in patients with acute ischemic stroke: a second analysis based on a prospective cohort study

ObjectiveEvidence regarding the relationship between serum triglyceride-to-high density lipoprotein cholesterol (TG/HDL-c) ratio and outcomes in acute ischemic stroke (AIS) patients is still mixed. Therefore, the present study was undertaken to explore the link between the TG/HDL-c ratio and unfavorable outcomes in patients with AIS.MethodsThis was a second analysis based on a cohort study. The study population was 1764 patients with AIS collected from January 2010 to December 2016 at a hospital in South Korea. We used a binary logistic regression model to assess the linear association between the TG/HDL-c ratio and unfavorable outcomes for AIS patients. A generalized additive model (GAM) and smooth curve fitting (penalized spline method) was conducted to explore the nonlinear relationship between TG/HDL-c ratio and unfavorable outcomes for AIS patients. Additionally, we compute the inflection point using a recursive algorithm and then build a two-piece binary logistic regression model on both sides of the inflection point. A log-likelihood ratio test was used to determine the most appropriate model describing the association of TG/HDL-c ratio and unfavorable outcomes in patients with AIS.ResultsThe incidence rate of unfavorable outcomes was 28.2%, and the median TG/HDL-c ratio was 2.130. After adjusting covariates, the results of the binary logistic regression model suggested that the relationship between the TG/HDL-c ratio and the risk of unfavorable outcomes for AIS patients was not statistically significant. However, there was a nonlinear relationship between them, and the inflection point of the TG/HDL-c ratio was 3.515. On the left side of the inflection point, each 1-unit increase in the TG/HDL-c ratio was associated with a 22.6% lower risk of unfavorable outcomes (OR = 0.774, 95%CI:0.656 to 0.914, p = 0.002). On the right side of the inflection point, the effect size (OR) was 1.195 (95%CI:1.004 to1.423, p = 0.003).ConclusionThere is a nonlinear relationship and threshold effect between the TG/HDL-c ratio and 3-month unfavorable outcomes in AIS patients. When the TG/HDL-c ratio is lower than 3.515, the TG/HDL-c ratio is significantly negatively related to the risk of unfavorable outcomes. When the TG/HDL-c ratio is greater than 3.515, the TG/HDL-c ratio was positively associated with the risk of unfavorable outcomes in AIS patients. This provides a reference for optimizing lipidemia intervention and promoting clinical communication in patients with AIS.

Identification of Major Risk Factors and Non-linear Effects to the Development of Left Ventricular Hypertrophy in Chronic Kidney Disease by Constructing and Validation of Nomograms

BackgroundLeft ventricular hypertrophy (LVH) is a common cardiovascular complication among chronic kidney disease (CKD) patients. The present study aimed to identify major independent risk factors and determine their contribution and relationship to LVH development.MethodsClinical and echocardiographic data of 2002 pre-dialytic CKD patients were retrospectively collected. Independent risk factors for LVH were identified using univariable and multivariable logistic regression. Nomograms together with restricted cubic splines method were employed to explore the effect size and possible non-linear relationship with regard to LVH. A simplified predictive model was constructed and its predictive ability was validated to demonstrate to which extent the identified risk factors accounted for LVH risk.ResultsMultivariable logistic regression identified age, body mass index (BMI), systolic blood pressure (SBP), eGFR and hemoglobin as independent influencing factors for LVH. Nomogram revealed BMI, SBP and hemoglobin concentration as the most important risk factors. Impaired renal function only showed obvious risk for LVH when eGFR declined below 30 ml/min/1.73 m2. Significant threshold effects existed for blood pressure and obesity that the risks for LVH doubled when SBP exceeded 160 mmHg or BMI exceeded 30 kg/m2. The predictive model constructed performed well on both the training and validation cohort using calibration curve, ROC curve and AUC value, with AUC above 0.80 for both the training cohort and the validation cohort.ConclusionsWith the help of nomogram model, we identified five independent factors that explain a large proportion of LVH risk in CKD patients. Among them, major contribution to LVH development was resulted from comorbidities and complications of CKD (hypertension, anemia, obesity) rather than eGFR reduction per se. Non-linear relationship and threshold relationship between eGFR, blood pressure, obesity and LVH risk were also identified.

Financial development, technological innovation and energy security: Evidence from Chinese provincial experience

Rapid growth in the demand for global energy has raised concerns about energy security and climate change. Based on statistical data of 30 provinces in China from 2000 to 2018, this paper takes energy security as the focus, adopting a fixed effect model, random effect model, instrumental variable estimation, and panel threshold model to systematically verify the influence of the relationship between financial development, technological innovation, and their interaction term on energy security. Through a series of empirical analyses, endogeneity tests, and robustness tests, the findings suggest that China's energy security is enhanced by financial development and technological innovation. Specifically, financial development can improve energy security through technological innovation. At the same time, there is a nonlinear threshold effect between financial development and energy security due to differences in technological innovation between regions. Further heterogeneity analysis shows that the constraint of technological innovation is significantly supported in coastal regions and regions with low capital stock. The empirical results of this paper provide policy recommendations and empirical insights for China's energy security.

Debt Sustainability in Developing Economies: Evidence from Sub-Sahara Africa

In this study, we assess the debt sustainability of emerging economies in Sub-Saharan Africa. We specify a dynamic panel threshold to estimate the debt threshold for primary surplus and economic growth. The results reveal a non-linear threshold effect. First, with a threshold value of 17.95%, the primary surplus has a strong positive relationship with the debt-to-GDP ratio. Second, economic growth is maintained when the debt-to-GDP ratio is about 52%. The study recommends that governments in SSA should make conscious efforts to restore fiscal discipline that will keep the debt burden at a rate reasonable enough to sustain and avoid debt overhang problems.

Origin of Nonlinear Damping Due to Mode Coupling in Auto-Oscillatory Modes Strongly Driven by Spin-Orbit Torque

We investigate the physical origin of nonlinear damping due to mode coupling between several auto-oscillatory modes driven by spin-orbit torque in constricted Py/Pt heterostructures by examining the dependence of auto-oscillation on temperature and applied field orientation. We observe a transition in the nonlinear damping of the auto-oscillation modes extracted from the total oscillation power as a function of drive current, which coincides with the onset of power redistribution amongst several modes and the crossover from linewidth narrowing to linewidth broadening in all individual modes. This indicates the activation of another relaxation process by nonlinear magnon-magnon scattering within the modes. We also find that both nonlinear damping and threshold current in the mode-interaction damping regime at high drive current after transition are temperature independent, suggesting that the mode coupling occurs dominantly through a non-thermal magnon scattering process via a dipole or exchange interaction rather than thermally excited magnon-mediated scattering. This finding presents a promising pathway to overcome the current limitations of efficiently controlling the interaction between two highly nonlinear magnetic oscillators to prevent mode crosstalk or inter-mode energy transfer and deepens understanding of complex nonlinear spin dynamics in multimode spin wave systems.

Quantifying the environmental limits to fire spread in grassy ecosystems

Modeling fire spread as an infection process is intuitive: An ignition lights a patch of fuel, which infects its neighbor, and so on. Infection models produce nonlinear thresholds, whereby fire spreads only when fuel connectivity and infection probability are sufficiently high. These thresholds are fundamental both to managing fire and to theoretical models of fire spread, whereas applied fire models more often apply quasi-empirical approaches. Here, we resolve this tension by quantifying thresholds in fire spread locally, using field data from individual fires (n = 1,131) in grassy ecosystems across a precipitation gradient (496 to 1,442 mm mean annual precipitation) and evaluating how these scaled regionally (across 533 sites) and across time (1989 to 2012 and 2016 to 2018) using data from Kruger National Park in South Africa. An infection model captured observed patterns in individual fire spread better than competing models. The proportion of the landscape that burned was well described by measurements of grass biomass, fuel moisture, and vapor pressure deficit. Regionally, averaging across variability resulted in quasi-linear patterns. Altogether, results suggest that models aiming to capture fire responses to global change should incorporate nonlinear fire spread thresholds but that linear approximations may sufficiently capture medium-term trends under a stationary climate.

Applying Decision Trees to Examine the Nonlinear Effects of Multiscale Transport Accessibility on Rural Poverty in China

Accessibility plays an important role in alleviating rural poverty. Previous studies have explored the relationship between accessibility and rural poverty, but they offer limited evidence of the collective influence of multiscale transport accessibility (town-level, county-level, and prefecture-level accessibility) and its nonlinear effects on rural poverty. This study adopted the gradient-boosting decision tree model to explore the nonlinear association and threshold effects of multiscale transport accessibility on the rural poverty incidence (RPI). We selected Huining, a poverty-stricken county in China, as a case study. The results show that multiscale transport accessibility collectively has larger predictive power than other variables. Specifically, town-level accessibility (12.97%) plays a dominant role in predicting the RPI, followed by county-level accessibility (9.50%) and prefecture-level accessibility (7.38%). We further identified the nonlinear association and effective ranges of multiscale transport accessibility to guide poverty-alleviation policy. Our results help inform policy and planning on sustainable poverty reduction and rural vitalization.

Strategic leadership, environmental optimisation, and regional innovation performance with the regional innovation system coupling synergy degree: evidence from China

ABSTRACT This study investigates the impact mechanism of the government’s strategic leadership (SL) and environmental optimisation (EO) on the improvement of regional innovation performance (RIP) under the effects of the regional innovation system coupling synergy degree (RISCSD). Based on the nonlinear threshold regression model, the coupling synergy model and entropy value method, the threshold regression analysis is conducted by calculating the RISCSD. The results indicate that: under the effect of the RISCSD, the SL, EO, and RIP have distinct single and double threshold effects. With the improvement of RISCSD, the influence of SL on RIP has changed from inhibition to promotion; while the promotion effect of EO on RIP shows an upward trend at first, and then slightly weakening. This paper provides relevant policy suggestions for local public administrations to enhance RIP.

Above bandgap one-photon excitation induced nonlinear absorption behavior of InTe

In an attempt to investigate the nonlinear absorption properties of amorphous InTe semiconductors, three different thicknesses of 30 nm, 60 nm and 90 nm thin films were deposited by the vacuum evaporation method. Bandgap energies and Urbach energies were obtained from the linear absorption spectrum. While the change in thickness and doping led to slight changes in bandgap energies as 0.08 eV, significant increases in Urbach energies were obtained for thicker and doped films. A theoretical model accounting one photon absorption, excited state absorption, and saturation of each process was utilized to derive the transmittance in open aperture Z-scan data. The values of nonlinear absorption coefficient and saturation intensity threshold were obtained from the model and the interplay between excited state absorption and saturable absorption was explained by proposing an energy band diagram containing the contribution of defect states to the nonlinear absorption behavior of amorphous semiconductors.

Linear approximation of the Threshold AutoRegressive model: an application to order estimation

This paper proposes a linear approximation of the nonlinear Threshold AutoRegressive model. It is shown that there is a relation between the autoregressive order of the threshold model and the order of its autoregressive moving average approximation. The main advantage of this approximation can be found in the extension of some theoretical results developed in the linear setting to the nonlinear domain. Among them is proposed a new order estimation procedure for threshold models whose performance is compared, through a Monte Carlo study, to other criteria largely employed in the nonlinear threshold context.

Ultra-Low-Noise MIMO Distributed Acoustic Sensor Using Few-Mode Optical Fibers

Distributed optical fiber acoustic sensing technology (DAS) based on Rayleigh backscattering (RBS) is experiencing a rapid development because of the unique capability of measuring acoustic waves along long-distance optical fiber with high spatial resolution, that has broad prospects of applications, including geophysical prospecting, seismology, pipeline security, and train tracking. Despite the numerous applications, DAS currently suffers from high noise level and insufficient signal-to-noise ratio (SNR) due to inherent low RBS coefficient (&#x223C; &#x2212;70 dB&#x002F;m) in fiber, and cannot meet the application requirements of weak signal detection. Here, an ultra-low-noise MIMO DAS system using few-mode fibers (FMF) is proposed. FMF is characterized by higher non-linear effect threshold and larger capture fraction of RBS light, and through MIMO technology, the system can realize higher diversity scale and obtain more SNR gain. In addition, &#x2018;frequency label&#x2019; method is proposed to address the signal aliasing problem in transmission modes. In preliminary experiments, a 4&#x00D7;4 MIMO &#x03A6;-OTDR system is realized, where the minimum noise floor is &#x2212;88 dB rad²&#x002F;Hz with corresponding strain resolution of 0.15 <inline-formula><tex-math notation="LaTeX">$p\varepsilon /\sqrt {Hz} $</tex-math></inline-formula>. These results pave the way for advanced acoustic applications of DAS, such as acoustic emission and marine acoustics.

Oil price volatility forecasting: Threshold effect from stock market volatility

Stock market volatility, which is usually considered a proxy for the general economy, contains important information for the crude oil market. In this paper, we investigate the incremental benefit of stock market volatility over oil volatility using the S&P 500 index and WTI oil prices for the period from January 1990 to December 2021. The threshold autoregressive regression (TAR) model is used to capture the nonlinear threshold effect of stock market shock on oil market volatility. From empirical analysis, both in-sample and out-of-sample results highlight the prediction superiority and effectiveness of the nonlinear threshold regression model, which indicates the valuable strong threshold effects of stock volatility for oil volatility forecasting. Moreover, the additional effects of stock volatility in terms of bad volatility forecasting further confirm the effectiveness of the nonlinear TAR model and the information content of stock volatility. This study will prove useful for policy-makers to formulate reasonable policies and for investors to avoid risk.