Incoherent Effects Research Articles

The effect of methyl group rotation on 1H-1H solid-state NMR spin-diffusion spectra.

Fast magic-angle spinning (MAS) NMR experiments open the way for proton-detected NMR studies and have been explored in the past years for a broad range of materials, comprising biomolecules and pharmaceuticals. Proton-spin diffusion (SD) is a versatile polarization-transfer mechanism and plays an important role in resonance assignment and structure determination. Recently, the occurrence of negative cross peaks in 2D 1H-1H SD-based spectra has been reported and explained with higher-order SD effects, in which the chemical shifts of the involved quadruple of nuclei need to compensate each other. We herein report negative cross peaks in SD-based spectra observed for a variety of small organic molecules involving methyl groups. We combine experimental observations with numerical and analytical simulations to demonstrate that the methyl groups can give rise to coherent (SD) as well as incoherent (Nuclear Overhauser Enhancement, NOE) effects, both in principle manifesting themselves as negative cross peaks in the 2D spectra. Analytical calculations and simulations however show that higher-order coherent contributions dominate the experimentally observed negative peaks in our systems. Methyl groups are prone to the observation of such higher order coherent effects. Due to their low-frequency shifted 1H resonances, the chemical-shift separation relative to for instance aromatic protons in spatial proximity is substantial (>4.7 ppm in the studied examples) preventing any sizeable second-order spin-diffusion processes, which would mask the negative contribution to the peaks.

Influence of uncertainty of structural parameters on the stochastic dynamic response of asphaltic lining dam-foundation systems to non-stationary random seismic excitation

The present work aims toward the effect of uncertain structural parameters on the stochastic dynamic response of an asphaltic lining dam-foundation system subjected to stationary as well as non-stationary random excitation. Uncertain structural parameters of interest are shear modulus and mass density, modeled using the lognormal distribution. The stochastic seismic response of the dam-foundation system to the random loads with uncertain structural parameters is carried out with the Monte Carlo simulation method. The spatial variability of ground motion is considered with incoherence and wave passage effects as stationary as well as non-stationary random excitation. A time-dependent frequency response function is used throughout the study for non-stationary responses. Obtained results indicate that the variability of shear modulus and mass density can be neglected in stochastic dynamic analysis of an asphaltic lining dam-foundation system. Also, it is seen from the results that stationarity is a reasonable assumption for asphaltic lining dams to typical durations of strong shaking.

A Review on the Combined Effects of Seismic and Vehicular Vibrations on Long Span Bridges

Long span bridges are massive structures which are subjected to combined loadings. The increase in span length of long span bridges will result in decrease of their natural frequencies that renders them very susceptible to the actions of various combined dynamic forces. Dynamic loads such as vehicular movement and seismic excitations have greater potential in causing increased vibrations in long span bridges. The vehicular loading is highly variable and depends on type of vehicle, number of lane, behaviour of vehicle such as lane changing, traffic congestions and so on. Further, seismic excitations are characterized by its spatial variability parameters such as incoherence effect, wave passage effect and site response effects. From detailed review, it was found that fewer researches have been carried out in the field of dynamic effects of long span arch bridges and thus the study aims in determining the combined effects of seismic and vehicular vibrations on long span arch bridges.

Identifying incoherent mixing effects in the coherent two-dimensional photocurrent excitation spectra of semiconductors.

We have previously demonstrated that in the context of two-dimensional (2D) coherent electronic spectroscopy measured by phase modulation and phase-sensitive detection, an incoherent nonlinear response due to pairs of photoexcitations produced via linear excitation pathways contributes to the measured signal as an unexpected background [Grégoire et al., J. Chem. Phys. 147, 114201 (2017)]. Here, we simulate the effect of such incoherent population mixing in the photocurrent signal collected from a GaAs solar cell by acting externally on the transimpedance amplifier circuit used for phase-sensitive detection, and we identify an effective strategy to recognize the presence of incoherent population mixing in 2D data. While we find that incoherent mixing is reflected by the crosstalk between the linear amplitudes at the two time-delay variables in the four-pulse excitation sequence, we do not observe any strict phase correlations between the coherent and incoherent contributions, as expected from modeling of a simple system.

On the effect of incoherence in a polarized dusty plasma and Wigner stability

We theoretically analysed the effect of incoherence present in the initial density in a homogeneous plasma containing nonthermal ions and Maxwellian electrons under the influence of polarization force. The Krylov-Bogoliubov-Mitropolsky (KBM) method is used to derive the Nonlinear Schrödinger equation. In the next stage the incoherence effect is analysed by studying the equation of motion of the correlation function 〈n(x, t)n *(x, t)〉 with the help of Wigner quantization and Moyal braket. The modulational stability of the new equation is exhaustively studied with respect to the plasma parameters variation and the effect of polarization force. In the next section, we considered a q-nonextensive distribution of electrons and viewed a more general form of polarization force by following Bentabet et al. The same analysis is again repeated and the modulation stability is analysed.

Application of an integrated nonuniform seismic random excitation method in tunnel engineering in soft soil areas

Nonuniform seismic excitation cannot be neglected in the seismic design of long-span tunnels in soft soil areas, as it might induce tunnel damage. This paper proposes a method that combines an integrated nonuniform seismic random excitation method with the finite element method to solve the problem of nonuniform seismic input for geotechnical tunnel seismic design in soft soil areas. The integrated nonuniform seismic random excitation method of producing multipoint random seismic waves is investigated considering the effects of passage, incoherence, and energy attenuation. Design codes are developed to achieve random seismic ground waves, baseline adjustment and filtering, and inversion of bedrock. The correctness of an integrated nonuniform seismic random excitation is verified by analysis of the differences (5%–10%) between the simulated and theoretical power spectrum functions. Based on this modelling, the dynamic responses of tunnels subjected to longitudinal and lateral seismic excitations are investigated. Nonuniform seismic excitation will cause greater tunnel deformation and internal forces than uniform seismic excitation due to the tunnel consuming more seismic energy under nonuniform seismic excitation. Longitudinal nonuniform seismic excitation induces compressive and tensile states in the tunnel, and the maximum tension is close to the tensile strength of the concrete. Lateral nonuniform seismic excitation can enlarge the bending moment and shear force, and bending moment and shear force distribution ranges are recommended for this case study.

Seismic Response Analysis of Bongo Bridge Subjected to Multiple Support Excitation due to Spatial Variation of Ground Motion

The spatial variation of ground motion (SVGM) may cause detrimental effects on extended structures such as bridges. The SVGM is mainly caused by three phenomena: the incoherence effect, wave passage effect, and the local site effect, which leads the structure to undergo multiple support excitation. In most cases, in the Philippines, the conventional response spectrum analysis per DPWH Bridge Seismic Design Specifications (BSDS) 2013 is used to perform seismic analysis of bridges. However, the method assumes that the ground motion is spatially uniform, thus ignoring the potential effect of SVGM. The study focuses on the seismic response analysis of a conventional existing highway bridge in the Philippines subjected to multiple support excitation accounting for the effect of SVGM. The researcher used the Bongo Bridge located in Ilocos Norte, originally designed using the conventional response spectrum. A method for generating a modified response spectrum that accounts for the effect of SVGM based on the fundamental principle of random vibration theory was also presented to provide guidelines for bridge engineers in the Philippines. Three cases were performed where each seismic response of the existing bridge was obtained and evaluated to determine if the application of multiple support excitation due to SVGM will cause a significant effect on the existing bridge. Based on the results, the effect of multiple support excitation to Bongo Bridge amplified the seismic response of some pier columns and de-amplified some. The study also shows that the effect of multiple support excitation decreased the displacement demand significantly on the Bongo Bridge. Since the study is limited to Bongo Bridge and the seismic response can be affected by many factors, the result may vary to other bridges. Therefore, it is still recommended to perform a parametric analysis accounting for multiple support excitation especially if the structure is situated on a varying ground type or bridges with multiple and longer spans, to determine if this phenomenon will cause a significant effect on the bridge.

The Goos Hänchen shifts in the reflection/transmission beams under Kerr nonlinearity, Doppler broadening and Compton scattering

Reflection, transmission as well as absorption coefficients and the corresponding Goos Hänchen shift in reflection and transmission is controlled and modified under the effects of Kerr nonlinearity, Doppler broadening as well as Compton scattering. The summation of the absolute values of these coefficients gives a unit value in the presence of all these effects. Modification of the coefficients follows the normalization condition. Maximum GH-shift in the reflection/transmission is investigated to ±3λ. Above ϕc=π/6, the GH-shift is saturated at the value λ in both reflection/transmission. The positive as well as negative GH-shift is measured in the absence and presence of Compton scattered reflected/transmitted beam. The GH-shift is the function of control fields, Kerr nonlinearity, incoherent effect of Doppler broadening and incident as well as the Compton scattered angles. The results show potential applications in nano-optics, trapping of optical data, micro-optics, acoustics, sensor technology and plasma physics.

Compressible Test-field Method and Its Application to Shear Dynamos

In this study, we present a compressible test-field method (CTFM) for computing α-effect and turbulent magnetic diffusivity tensors, as well as those relevant for the mean ponderomotive force and mass source, applied to the full MHD equations. We describe the theoretical background of the method and compare it to the quasi-kinematic test-field method and to the previously studied variant working in simplified MHD (SMHD). We present several test cases using velocity and magnetic fields of the Roberts geometry and also compare with the imposed-field method. We show that, for moderate imposed-field strengths, the nonlinear CTFM (nCTFM) gives results in agreement with the imposed-field method. A comparison of different flavors of the nCTFM in the shear dynamo case also yields agreement up to equipartition field strengths. Some deviations between the CTFM and SMHD variants exist. As a relevant physical application, we study nonhelically forced shear flows, which exhibit large-scale dynamo action, and present a reanalysis of low-Reynolds-number, moderate shear systems, where we previously ignored the pressure gradient in the momentum equation and found no coherent shear-current effect. Another key difference is that in the earlier study we used magnetic forcing to mimic small-scale dynamo action, while here it is self-consistently driven by purely kinetic forcing. The kinematic CTFM with general validity forms the core of our analysis. We still find no coherent shear-current effect, but do recover strong large-scale dynamo action that, according to our analysis, is driven by incoherent effects.

Multiple Andreev reflections effect spectroscopy of LiFeAs single crystals: three superconducting order parameters and their temperature evolution

The structure of the superconducting order parameter of LiFeAs is studied by incoherent multiple Andreev reflections effect (IMARE) spectroscopy. The high transparent superconductor–thin normal metal–superconductor (SnS) contacts are created by a planar “break-junction” technique. Below T_c approx 17.5 K, the obtained I(V) and dI(V)/dV characteristics of SnS junctions show a presence of at least three bulk superconducting order parameters in LiFeAs. We directly determine the magnitudes, characteristic ratios, and temperature dependences of the superconducting gaps and discuss their symmetry.

Fragility Analysis of RC Bridges Considering Spatially Varying Ground Motions and SSI

Long-span structures like bridges experience different movements at the supports because of the wave-passage, incoherence, and site-response effects. In this study, spatially varying ground motions were used to evaluate the seismic vulnerability of different RC bridges. To gain the goal, three prototypes of Caltrans reinforced concrete curve bridges with different column heights and various radii were selected and used for the numerical study. The spatially correlated ground motions were generated by the conditional simulation method and then converted to corresponding displacements time histories to perform non-uniform excitations. The structures were analyzed under generated series and the fragility curves were developed based on the defined limit states. Furthermore, soil-structure interactions and different soil conditions were included in evaluating the non-linear behavior of the bridges. The results show that the damage exceedance probability increased under non-uniform excitations and it is more obvious for long-span bridges. Also, it is found that the effect of soil-structure interactions on the probability of failure of short-span bridges is negligible but for long-span bridges, the effect is significant. Moreover, it is obvious that for long-span structures situated on soft deposits, a combination of spatially varying ground motions in conjunction with soil-structure inter-actions remarkably increases the responses.

Divergent desires for the just transition in South Africa: An assemblage analysis

In this paper I establish a ‘just transition assemblage’ as a theoretical and empirical case-study to explore the plurality of justice in South Africa's energy transition. The coal phase-out is complicated by the legacies of apartheid, poverty, inequality, unemployment and structural crisis in the state-owned power utility. This transition is loaded with expectation but there is no consensus on what would qualify it as ‘just’. This assemblage analysis clusters desires around two distinct post-carbon imaginaries. The first is an ordering of desires for justice in a diffuse, distributional sense, targeting greenhouse gas emission reductions and looking to smooth the negative impacts of the transition. I label this approach ‘net justice’. This targets more justice overall in defined political spaces, and contrasts with the second orientation around recognising, reconciling, and addressing specific injustices. These desires are distinguished by a contrasting purpose of renewable energy and differing attitudes to its appropriateness or fit. There are incoherent spatial effects, where net justice is shown to be a territorialising project whilst specific injustices need to be de-territorialised. Emphasising desire shows how material and history are enrolled and enlivened, contributing to post-carbon imaginaries. This approach enables injustice and net justice to be understood as conceptually distinct, despite seeming unified calls for a just transition. The primary contribution of this paper is to show how in some cases, popular uses of the terms justice and injustice refer to different things. It forces attention on the question of: ‘justice for whom?’

Investigation of near cut‐off properties of electromagnetic wave propagation in homogeneous, collisional plasma slab

AbstractFluctuations in the signal of optical coefficients of propagative electromagnetic (EM) waves in plasma, can cause problems in phase analysis, especially in microwave diagnostic systems which are based on the reflection, and transmission of EM waves in the vicinity of cut‐off layer of the plasma. In this study, optical properties of EM wave propagation in a single layer, homogeneous, and partially ionized plasma slab are investigated. For realistic analysis of propagation characteristics of the EM wave in the plasma slab, multiple reflections of the EM wave from plasma‐vacuum boundaries, known as incoherent internal reflections (IIR) are considered. Optical coefficients of the EM wave are numerically simulated in terms of the plasma parameters and wave frequency, with and without consideration of the incoherent internal reflections effect. It was found that in the low‐loss collision regime, the cut‐off fluctuations of the optical coefficients can be filtered considering the incoherent internal reflections of the EM wave. Such analysis of the EM wave propagation in plasma slab can be considered the primary physical design of diagnostic facilities and EM wave absorbing structures operating in the cut‐off frequency ranges.

Topological Quantum State Control through Exceptional-Point Proximity.

We study the quantum evolution of a non-Hermitian qubit realized as a submanifold of a dissipative superconducting transmon circuit. Real-time tuning of the system parameters to encircle an exceptional point results in nonreciprocal quantum state transfer. We further observe chiral geometric phases accumulated under state transport, verifying the quantum coherent nature of the evolution in the complex energy landscape and distinguishing between coherent and incoherent effects associated with exceptional point encircling. Our work demonstrates an entirely new method for control over quantum state vectors, highlighting new facets of quantum bath engineering enabled through dynamical non-Hermitian control.

Higher-order optical rogue waves in spatially inhomogeneous multimode fiber

The objective is to explore the mathematical analysis to understand and manipulate the dynamics of higher-order rogue waves in an inhomogeneous multi-mode optical media. For this purpose, we consider a theoretical model represented by the coupled nonlinear Schrödinger equations consisting of the spatially varying dispersion and nonlinearities arising from both coherent and incoherent nonlinear effects, which drives the spatially modulated linear and nonlinear refractive index of the media. We construct controllable spatiotemporally (doubly) localized rogue wave solutions through Darboux transformation and by designing a similarity transformation. Explicitly, we investigate the evolution of first- and second-order vector rogue waves possessing different characteristics such as degenerate and non-degenerate type bright, gray, and dark localized profiles that can be controlled by the inhomogeneity arising in the medium and polarization parameters available in the solutions. To highlight the consequences of the spatially inhomogeneous nature of the medium, we demonstrate the transition mechanism of rogue waves by adopting four different spatial modulations, namely periodic, hyperbolic, and localized behavior, by incorporating Jacobi elliptic functions. Significantly, these modulations lead to the transition of rogue waves to spatially-periodic Akhmediev breathers of single- and multi-peak symmetric and asymmetric behavior arising on top of snoidal, cnoidal, and dnoidal backgrounds. Further, the rogue waves experience amplification, suppression, splitting, and trapping due to localized soliton type background modulations. The observed results will facilitate improvement in understanding other types of localized nonlinear waves in different inhomogeneous media.

Optical bistability in a negative refractive index media using the electron tunneling effect

In this letter, we proposed a brand-new version for investigating the optical bistability (OB) and optical multistability (OM) through electron tunneling impact in a defect one-dimensional photonic crystal (1DPC). The defect layer of 1DPC is doped with double quantum dot (DQD) nanostructure which interacts with an indirect incoherent pump and a susceptible probe incident light, respectively. By the usage of the quantum mechanical density matrix method, we first examine the refractive index properties of the defect layer through electron tunneling and indirect incoherent pumping effects. Then, through the usage of the transfer matrix methods, we acquire the reflection and transmission coefficients of the defect 1DPC. At the end, we discuss the OB and OM properties of the reflected and transmitted lighting in negative refractive index situation of the DQD. We determine that during a few parametric conditions the switching from OB to OM or vice versa is feasible for reflected and transmitted light beams.

Incoherent control of Goos–Hänchen shifts in a tunneling quantum dot molecule

In this letter, we propose a novel model for adjusting the Goos–Hänchen shifts (GH) from a fixed cavity. A three-level double quantum dot (QD) molecule is doped in the cavity, which interacts with a probe laser field and an incoherent pumping rate. We initially investigate the refraction index of double QDs utilizing the quantum mechanical density matrix approach in order to achieve negative and positive refractive indexes. The GH shifts of reflected and transmitted light beams in positive and negative refraction indices of the intracavity medium were then studied. The improved negative or positive GH shifts in reflected and transmitted light beams may be accomplished by changing the incoherent pumping rate and tunneling effect. Our findings reveal that the magnitude of the GH shifts is greatly influenced by the absorption of incoming probing light in double QDs. The enormous GH shifts for the perfect tuning cavity have been seen at a given incidence angle.

Reducing the noise of fiber supercontinuum sources to its limits by exploiting cascaded soliton and wave breaking nonlinear dynamics

The low-noise and phase-coherent nonlinear transformation of a narrowband laser into a broadband supercontinuum (SC) in an optical fiber forms the basis of extremely precise applications ranging from optical frequency comb technology to ultrafast photonics and biomedical imaging. A major challenge of this process is the avoidance of incoherent nonlinear effects that amplify random quantum noise, requiring careful birefringence and dispersion engineering of the fiber. However, fundamental trade-offs exist between working in normal or anomalous dispersion regimes. Here, we combine the benefits of nonlinear dynamics in both regimes by cascading soliton compression and optical wave breaking in a hybrid fiber, formed by joining two widely available, commercial, polarization-maintaining step-index fibers exhibiting anomalous and all-normal dispersion, respectively. We experimentally demonstrate that this hybrid approach results in an ultra-low-noise fiber SC source covering the 930–2130 nm range with phase coherence near unity, spectrally resolved relative intensity noise (RIN) as low as 0.05%, and averaging 0.1% over a bandwidth of 750 nm, approaching the theoretical limits close to the pump laser noise. This corresponds to a doubling of the generated spectral bandwidth and a decrease of RIN by up to 1 order of magnitude compared to direct pumping of the individual fibers, where modulational polarization instabilities play a limiting role. Owing to its simplicity and its scalability to high repetition rates, our hybrid scheme is readily applicable to various laser platforms and could enhance the performance of applications such as hyperspectral nonlinear microscopy, coherent optical communications, and photonic signal processing.

Iterative method for optical modelling of perovskite-based tandem solar cells.

We present an iterative method to model the optical properties of a complete semitransparent perovskite solar cell. It is based on spectroscopic characterizations and accounts for porosity and incoherence effects. We provide the complex refractive indices of each layer, and we identify the main sources of optical losses. The optical model is also coupled to an electrical model of 4T perovskite/silicon tandem solar cells. It allows to evaluate the interplay between the optical and electrical losses, and the balance between the efficiency of the top and bottom cells. These models provide an effective way to design future tandem devices.

On the role of bandwidth in pump and seed light waves for stimulated Raman scattering in inhomogeneous plasmas

The effects of incoherence on the three-wave coupling process of backward stimulated Raman scattering (SRS) in inhomogeneous plasmas are investigated theoretically and numerically via a three-wave coupling model. The impact of the plasma wave nonlinearity is taken into account, namely, the effect of trapped electrons via a nonlinear frequency shift of the electron plasma wave. Incoherence in the coupling is introduced in the seed wave, and the laser pump wave via bandwidth associated with a Lorentzian power spectrum. It is found that temporal incoherence can suppress the instability as long as the gain associated with spatial amplification in an inhomogeneous plasma (“Rosenbluth gain”) is smaller than 2. Otherwise, kinetic effects may destabilize SRS and significantly increase the backscatter level. For the bandwidth effects of the pump laser, a statistical analysis has been performed to examine the real impact of bandwidth. Moreover, a semi-analytical expression of the growth rate in the nonlinear stage is given. By estimating the bandwidth effects, it is found that a broad bandwidth of the pump laser starts to mitigate the scattering provided that the laser beam coherence time τc is shorter than γ0−1, the inverse of the standard SRS growth rate γ0. However, to obtain effective mitigation, by maintaining SRS in an almost linear stage, it is found that the criterion γ0τc≤0.35 has to be fulfilled.