Presence Of Nonlinear Effects Research Articles

Complex refractive index with the presence of nonlinear effects.

The refractive index during self-focusing was considered as a component of the metric tensor, it means, as a curvature of space-time. However, there was an interest – what will be, if the refractive index is complex. If we introduce a complex metric tensor, then the complex part will not curve space-time. At the same time, with the presence of nonlinear effects, damping modes will occur, it means, if n is linear, then the absorption will be α, but if n = n1 + n2I, then the absorption will be different, which will be discussed in this article.

Attachment to parental figures in emerging adults from Brazil, India, and Nigeria: Associations with anxiety and depressive symptoms

Attachment theory suggests that experiences with parents and other caregivers are relevant for psychological functioning into adulthood, especially in relation to anxiety and depressive symptoms. However, this work has largely focused on Western countries and has often neglected relationships with paternal figures. The goal of the current study was to test four competing models of parental figure attachment (monotropy, only one attachment relates to symptoms; hierarchical, one attachment is more strongly related to symptoms; independence, both attachments are uniquely important in different ways; and integration, both attachments are uniquely important and interactive) in emerging adults from three countries with different cultures and family structures. We recruited 324 Brazilian, 309 Indian, and 319 Nigerian emerging adults using the online survey platform BeSample. Participants reported attachment to parental figures (maternal and/or paternal), anxiety symptoms, and depressive symptoms. Response surface analyses were tested in each country separately. In general, the results supported an integration model with significant interactions between parental figures. However, the direction of this interaction, as well as the presence of non-linear effects, differed by country. Our results suggest caregiver attachment remains relevant for individuals during the transition to young adulthood but with cultural variations.

Exclusive Photo-production of J/Ψ and Ψ(2s) as a tool to explore the transition to high and saturated gluon densities at the LHC.


 
 
 We study the energy dependence of the cross-section for exclusive photo-production of vector mesons J/Ψ and Ψ(2s) and search for signs for the onset of non-linear QCD dynamics in this observable. Our study is based on two dipole models: the Golec-Biernat, Wuesthoff Model (GBW) and the Bartels, Golec-Biernat, Kowal- ski Model (BGK). We find that differences between linear and non-linear implementations of these models are relatively small in the kinematic region probed by both HERA and LHC experiments if the energy dependence of the photo-production cross-section is being considered. We however find that the ratio of both cross-sections grows with energy in the presence of non-linear effects, while it remains approximately constant in the linearized case. The ratio of photo-production cross-sections might therefore provide a suitable tool to characterize the size of non-linear QCD effects at current collider energies.
 
 

Предельно короткие оптические импульсы в среде ориентированных углеродных нанотрубок с нелинейностью 3 и 5 порядков

In the work, a theoretical study was carried out as well as numerical simulation of the interaction of three-dimensional extremely short pulses with an inhomogeneous array of oriented semiconductor carbon nanotubes, with polarization nonlinearities of 3 and 5 orders. The results of the temporal evolution of such pulses and the dependence of the pulse strength on the parameters of the inhomogeneity of an array of oriented nanotubes are shown. Extremely short pulses (ESP), in this case, mean optical pulses of high intensity, containing one to five periods of the electromagnetic field, with a duration of up to 100 ps. The pulse frequency lies in the near-infrared range. A necessary condition for the stable propagation of extremely short pulses is the presence of nonlinear effects that would make it possible to compensate for their dispersion and diffraction spreading. Therefore, an array of oriented carbon nanotubes (CNTs), which have nonlinear properties, was chosen as the pulse propagation medium. The use of nonlinear optical media can be used to create coherent radiation sources, light sources with variable frequency, etc.

Nonlinearity and lasing topological zero-mode in distorted photonic lattice

Recently we have witnessed experimental realization of a Majorana zero-mode bound at vortex distortion induced in bipartite hexagonal photonic lattices. Here, we address an open question of the impact of nonlinearity on the zero-mode dynamics by theoretically investigating the abilities of topologically protected zero-modes to guide, couple and lase light in the presence of nonlinear effects. Light-intensity related nonlinearity enters the scene through a local nonlinear lattice response and driving properties: saturable nonlinear gain and linear loss. We demonstrate an efficient steady zero-mode lasing regime by managing the lattice and driving parameters. Obtained results open up possibilities for design of new topological lasers in length-scalable photonic platforms, such as multicore optical fibers.

Enhanced phase mixing of torsional Alfvén waves in stratified and divergent solar coronal structures – II. Non-linear simulations

ABSTRACT We use magnetohydrodynamic (MHD) simulations to detect the non-linear effects of torsional Alfvén wave propagation in a potential magnetic field with exponentially divergent field lines, embedded in a stratified solar corona. In Paper I, we considered solutions to the linearized governing equations for torsional Alfvén wave propagation and showed, using a finite difference solver we developed named WiggleWave, that in certain scenarios wave damping is stronger than what would be predicted by our analytical solutions. In this paper, we consider whether damping would be further enhanced by the presence of non-linear effects. We begin by deriving the non-linear governing equations for torsional Alfvén wave propagation and identifying the terms that cause coupling to magnetosonic perturbations. We then compare simulation outputs from an MHD solver called Lare3d, which solves the full set of non-linear MHD equations, to the outputs from WiggleWave to detect non-linear effects such as: the excitation of magnetosonic waves by the Alfvén wave, self-interaction of the Alfvén wave through coupling to the induced magnetosonic waves, and the formation of shock waves higher in the atmosphere caused by the steepening of these compressive perturbations. We suggest that the presence of these non-linear effects in the solar corona would lead to Alfvén wave heating that exceeds the expectation from the phase mixing alone.

Vulnerabilities in the quantum key distribution system induced under a pulsed laser attack

Quantum communication protocols are considered secure provided that all devices included in the system are fully characterized, and side channels are closed. However, as a result of laser radiation exposure, it is possible to change quantum communication systems components’ characteristics. This leads to vulnerabilities appearing in the quantum key distribution system. In this paper, we consider the effect of pulsed laser radiation on fiber-optic isolators used in quantum communication systems. Isolators protect the source of the system from attacking optical radiation coming from the “eavesdropping” side via the quantum channel. Lowering the isolation factor can bring the entire system out of a secure state. This gives an eavesdropper access to information about the secret key. The scenario of the most probable attack to the source of the quantum key distribution system via a pulsed laser was simulated. The experimental setup provided exposure of fiber isolators with pulsed laser radiation at a wavelength of 1064 nm (within the transparency window of the isolators) with a mean power up to 840 mW in four different pulse generation modes. The isolation factor and throughput of tested samples were monitored using a laser diode with a wavelength of 1550 nm and average power of 10.5 mW. Spectrally selective splitters were used to separate the lasers. It is shown that the isolation factor (isolator attenuation in the direction from the quantum channel to the system) at a wavelength of 1550 nm decreases from the initial value of 59.1 dB to 24.5 dB. The throughput (in the direction from the system to the quantum channel) at the same wavelength decreases from 0.6 dB to 1.2–12.3 dB or remains the same, depending on the acting pulsed laser radiation parameters. Temperature monitoring showed that the temperature of the isolator body changes insignificantly when exposed to pulsed radiation. The obtained effects of changing the isolation coefficient and throughput can be explained by the presence of nonlinear effects in the magneto-optical crystal of the isolator. The results of the work can be applicable in the practical evaluation of quantum communication systems security, in particular, the security evaluation of quantum key distribution systems. The results can be used to prepare the standards for certification procedures for assessing the security of quantum communication systems. The work gives recommendations for enhancing signal source unit security in quantum communication systems. Namely, as countermeasures to protect against the effects of pulsed laser radiation, it is proposed to set optical fuses with a limited threshold power, detectors for monitoring input optical radiation power, and narrow-band optical filters at the entrance of the quantum communication system.

Bright and dark solitons of a weakly nonlocal Schrödinger equation involving the parabolic law nonlinearity

The search for soliton solutions of nonlocal Schrödinger equations in the presence of nonlinear effects has received special interest in the last few decades. In the present paper, a weakly nonlocal Schrödinger equation (WNSE) involving the parabolic law nonlinearity is considered and as a success, its soliton solutions including bright and dark solitons are constructed. Such a key goal is formally carried out using a series of efficient approaches such as Kudryashov and exponential methods (Their new versions). The results presented in this paper are of a significant role to describe the propagation of soliton waves in the weakly nonlocal parabolic law medium.

DSP-Assisted Nonlinear Impairments Tolerant 100 Gbps Optical Backhaul Network for Long-Haul Transmission.

High capacity long haul communication and cost-effective solutions for low loss transmission are the major advantages of optical fibers, which makes them a promising solution to be used for backhaul network transportation. A distortion-tolerant 100 Gbps framework that consists of long haul and high capacity transport based wavelength division multiplexed (WDM) system is investigated in this paper, with an analysis on different design parameters to mitigate the amplified spontaneous emission (ASE) noise and nonlinear effects due to the fiber transmission. The performance degradation in the presence of non-linear effects is evaluated and a digital signal processing (DSP) assisted receiver is proposed in order to achieve bit error rate (BER) of 1.56 × and quality factor (Q-factor) of 5, using 25 and 50 GHz channel spacing with 90 m effective area of the optical fiber. Analytical calculations of the proposed WDM system are presented and the simulation results verify the effectiveness of the proposed approach in order to mitigate non-linear effects for up to 300 km length of optical fiber transmission.

Personality traits as an engine of knowledge: a quantile regression analysis

PurposeWe use disaggregated survey data set to investigate the impact of personality traits on the level of education in the USA. We attempt to shed light on the contribution of each of the Big Five personality traits on the education decision made by the individuals.Design/methodology/approachWe use the quantile regression analysis in order to investigate to what extent certain aspects of personality may help an individual to invest in education.FindingsOur findings uncover a significant effect of noncognitive skills on the level of education. It is shown that people with high emotional stability and agreeableness invest in human capital, especially when we move to the higher quantiles of the conditional distribution function. Moreover, we argue that the estimated signs of the traits remain stable across the quantiles, while the relevant curvatures indicate for the first time in the empirical literature, the presence of nonlinear effects. Last, our model survived robustness checks under the inclusion of two aggregated higher-order factors, namely “Alpha” and “Beta.”Research limitations/implicationsAlthough we used several control variables (e.g. Gender, Age) to address the impact of noncognitive skills on education, special attention should be given to the use of additional socioeconomic indicators such as the skin color of participants, the urbanization rate, the level of unemployment, the level of income, parental education among others. These measures affect the causality driven by the inclusion of certain economic and demographic characteristics and minimize the endogeneity bias drawn from the inclusion of the sample variables. One additional limitation is that the survey-based data refer only to people with higher education (>13 years of study). Therefore, our empirical findings must be tested on a richer sample to capture the effect of personality traits on a broad spectrum of educational stages (e.g. early learning years, primary education, secondary education, etc.).Originality/valueOur empirical findings add enough new insights to the existing literature. First, we attempt to assess the role of noncognitive skills proxied by the Big Five Inventory (hereafter “BFI”) on the education decision made by the individuals. Second, we provide fresh evidence of nonlinear effects between personality traits and education totally ignored by the existing literature. Our third contribution is to analyze the role of personality in enhancing the importance of investment in higher education as a determinant of individual behavior. In this way, we contribute to the growing field of behavioral economics since the study of noncognitive skills offers a range of new ideas and expanding research opportunities for social scientists (economists, psychologists, sociologists, etc.).

Data-Driven Forecasting of Postflutter Responses of Geometrically Nonlinear Wings

Ensuring adequate flutter margins is a critical step in aircraft design. However, in the presence of nonlinear effects, subcritical limit-cycle oscillations can arise even before flutter occurs. When nonlinear effects are anticipated, postflutter analyses have to be integrated into aircraft design in addition to flutter computations for preventing this undesirable subcritical behavior. Therefore, there is a need for computationally fast postflutter analysis methods suitable for design applications. This paper investigates a data-driven method to forecast the bifurcation behavior of a geometrically nonlinear wing, demonstrating its suitability to analyze realistic nonlinear aeroelastic systems. The method efficiently forecasts postflutter responses using only a few system transient computations in the preflutter regime. First, the accuracy of forecasted bifurcation diagrams is verified against time-marching results. Next, wing design parameters are varied to investigate their impact on postflutter responses and show the method suitability to parametric studies.

Connections between resonance and nonlinearity in swimming performance of a flexible heaving plate

We investigate the role of resonance in finite-amplitude swimming of a flexible flat plate in a viscous fluid. The role of resonance in performance remains unclear for two reasons: i) a lack of definition of resonance for the fully-coupled fluid-structure interaction system in a viscous flow, and ii) the presence of nonlinear effects, which makes it difficult to disentangle resonant and non-resonant mechanisms in finite-amplitude swimming. We address point i) and provide an unambiguous definition for system resonance by computing global linear stability modes of the fully-coupled fluid-structure interaction system that account for the viscous fluid, the plate, and the coupling between them. We then resolve point ii) by considering high-fidelity nonlinear simulations of systematically increased amplitude. By comparing the results for different amplitudes with one another and with the linear stability modes, we separate linear and/or resonant effects from nonlinear and/or non-resonant effects. Resonant behavior is observed over a wide range of plate stiffnesses, with peaks in trailing-edge motion and thrust occurring near the resonant frequency defined by the global linear analysis. The peaks broaden and weaken with increasing heave amplitude, consistent with an increased damping effect from the fluid. At the same time, non-resonant mechanisms are present at large heave amplitudes. The input power exhibits qualitatively different dynamics at large heave amplitudes compared to smaller heave amplitudes, where resonance dominates. Moreover, leading-edge separation is present for stiff plates at large heave amplitudes, which can drastically alter the performance characteristics from what one would expect through linear predictions.

The Impact of Financial Development on Innovation Activities in Emerging and Developing Countries

We investigate in this paper the effect of financial development on innovation in emerging and developing countries. The estimation of panel threshold model for a sample 54 countries during the period 1980-2009 shows the presence of non linear effects in the relationship between financial development and innovation. We find a threshold value of economic development below which the financial development level has no significant impact on innovation and above which financial development has a significant positive impact on innovation. In sum, our findings suggest that the presence of a healthy economic environment is crucial for financial institutions to offer high-quality financial services, promoting more innovation.

New algorithm for the Guided Lock technique for a high-Finesse optical cavity

A known criticality of optical cavities such as Fabry–Pérot resonant cavities is the presence of non-linear effects in the build-up of the laser fields inside the cavity itself, which can spoil the characteristics of the error signal used to control the cavity length, usually obtained with the Pound–Drever–Hall phase modulation–demodulation technique. The non-linear effects are primarily caused by high cavity speeds prior to acquiring longitudinal control of the cavity (or “lock”), and they are due to the frequency fluctuations of the laser and to the residual seismic motion affecting the system; such effects are amplified with the increasing of the Finesse of the cavity. In order to overcome this limitation, the cavity speed is effectively slowed down before engaging the lock using a non-linear technique, known as “Guided Lock”; here an optimized version of the algorithm will be presented, which relies on a better estimation of the cavity speed based only on optical signals. The application of this technique to the high-Finesse Fabry–Pérot arm cavities of the Advanced Virgo gravitational wave detector will be described. The novel algorithm was applied for the lock acquisition of the Advanced Virgo detector during the O2 Observing Run, in August 2017; the improved algorithm, by dynamically measuring the cavity speed, allowed to implement a predictive capability in slowing down the mirrors, thus improving the efficiency of the lock acquisition procedure for the arm cavities.

Nonlinear Controller Design via Inferenced-Augmentation of Equivalent Linearized System

Output compensation of nonlinear system response is studied in this work with an inference-based design method used to control the nonlinear dynamics in the presence of non-linear effects. This design which is driven by practical considerations is informed by the comparisons made between nonlinear models and their linearized derivatives. While a detailed mathematical route has not been followed here, the results seem to show the workability of the proposed method and at its core, the design is driven by its intuitiveness. The proposed technique utilizes as primary parameter for comparison, the steady state error term which is derived from the behavior of the linear dynamics. Possible application areas for this design is in reduced energy control of nonlinear systems. The method was tested in simulation on a generic nonlinear system and a cart-driven inverted pendulum benchmark system.

Low-Complexity and Nonlinearity-Tolerant Modulation Format Identification Using Random Forest

A novel low-complexity and nonlinearity-tolerant modulation format identification (MFI) using random forest (RF) is proposed for the flexible coherent receivers (FCRs). The RF-based MFI takes the advantage of distinct features from the amplitude histograms (AHs) and the swarm intelligence of RF to significantly reduce the computational complexity compared with the deep learning-based method. Both numerical simulation and experiments are conducted. The simulation results of polarization multiplexed (PM) 4/8/16/32/64 quadrature amplitude modulation (QAM) wavelength division multiplexing (WDM) systems demonstrate its feasibility and identification performance. In the presence of nonlinear effects, with lower complexity than three other machine learning algorithms (k-nearest neighbors, support vector machine, and deep neural networks), the RF-based MFI can obtain 100% accuracy at the OSNR values greater than or equal to the respective soft decision forward error correction (SD-FEC) threshold. The identification accuracy versus total launch power is experimentally investigated in PM-4/16/32QAM WDM coherent systems. In the case of obvious nonlinear impairments, 100% accuracy can also be achieved above the OSNR corresponding to the SD-FEC threshold. The superiority of the proposed MFI method makes it highly desirable for applications in modulation format-adaptive FCRs.

Nonlinear optimal large-scale structures in turbulent channel flow

Coherent structures in turbulent shear flows take the form of packets of hairpin vortices reaching the outer region of the boundary layer along with streaks of different size, going from the near-wall to the outer region. The latter can be explained by the linear transient growth of the perturbations of the mean turbulent profile. Whereas, the former are recently found to be optimally-growing only in the presence of nonlinear effects, as ascertained for a turbulent channel flow at a low friction Reynolds number. The present work aims at investigating whether large-scale streaks can be optimally-growing in a nonlinear framework for a turbulent channel flow. Changing the friction Reynolds number from 180 to 590, the nonlinear optimal perturbation tends towards more robust large-scale streaks and vortical structures of smaller size. These streaks are generated by a coherent large-scale lift-up mechanism, acting as a source term in the energy balance, inducing a positive turbulent kinetic energy production at the outer scale. This indicates that the outer energy production peak arising between the two considered Reynolds numbers can be associated with the growth of optimal large-scale streaks, which represent a robust feature of turbulent channel flows.

High-dimensional multivariate additive regression for uncovering contributing factors to healthcare expenditure.

Many studies in health services research rely on regression models with a large number of covariates or predictors. In this article, we introduce novel methodology to estimate and perform model selection for high-dimensional non-parametric multivariate regression problems, with application to many healthcare studies. We particularly focus on multi-responses or multi-task regression models. Because of the complexity of the dependence between predictors and the multiple responses, we exploit model selection approaches that consider various level of groupings between and within responses. The novelty of the method lies in its ability to account simultaneously for between and within group sparsity in the presence of non-linear effects. We also propose a new set of algorithms that can identify inactive and active predictors that are common to all responses or to a subset of responses. Our modeling approach is applied to uncover factors that impact healthcare expenditure for children insured through the Medicaid benefits program. We provide important findings on the association between healthcare expenditure and a large number of well-cited factors for two neighboring states, Georgia and North Carolina, which have similar demographics but different Medicaid systems. We also validate our methods with a benchmark cancer data set and simulated data examples.

Estimation of Synaptic Conductances in Presence of Nonlinear Effects Caused by Subthreshold Ionic Currents.

Subthreshold fluctuations in neuronal membrane potential traces contain nonlinear components, and employing nonlinear models might improve the statistical inference. We propose a new strategy to estimate synaptic conductances, which has been tested using in silico data and applied to in vivo recordings. The model is constructed to capture the nonlinearities caused by subthreshold activated currents, and the estimation procedure can discern between excitatory and inhibitory conductances using only one membrane potential trace. More precisely, we perform second order approximations of biophysical models to capture the subthreshold nonlinearities, resulting in quadratic integrate-and-fire models, and apply approximate maximum likelihood estimation where we only suppose that conductances are stationary in a 50–100 ms time window. The results show an improvement compared to existent procedures for the models tested here.

Dynamically Encircling Exceptional Points: Exact Evolution and Polarization State Conversion.

We show that a two-level non-Hermitian Hamiltonian with constant off-diagonal exchange elements can be analyzed exactly when the underlying exceptional point is perfectly encircled in the complex plane. The state evolution of this system is explicitly obtained in terms of an ensuing transfer matrix, even for large encirclements, regardless of adiabatic conditions. Our results clearly explain the direction-dependent nature of this process and why in the adiabatic limit its outcome is dominated by a specific eigenstate-irrespective of initial conditions. Moreover, numerical simulations suggest that this mechanism can still persist in the presence of nonlinear effects. We further show that this robust process can be harnessed to realize an optical omnipolarizer: a configuration that generates a desired polarization output regardless of the input polarization state, while from the opposite direction it always produces the counterpart eigenstate.