Dispersion Terms Research Articles

Effect of intravalley and intervalley electron-hole exchange on the nonlinear optical response of monolayer MoSe2

The coherent third-order nonlinear response of monolayer transition-metal dichalcogenide semiconductors, such as ${\mathrm{MoSe}}_{2}$, is dominated by the nonlinear exciton response, as well as biexciton and trion resonances. The fact that these resonances may be spectrally close together makes identification of the signatures, for example in differential transmission (DT), challenging. Instead of focusing on explaining a given set of experimental data, a systematic study aimed at elucidating the roles of intravalley and intervalley long-range electron-hole $(e\ensuremath{-}\mathrm{h})$ exchange on the DT spectra is presented. Previous works have shown that the $e\ensuremath{-}\mathrm{h}$ long-range exchange introduces a linear leading-order term in the exciton dispersion. Based on a generalized Lippmann-Schwinger equation, we show that the presence of this linear dispersion term can reduce the biexciton binding energy to zero, contrary to the conventional situation of quadratic dispersion where an arbitrarily weak (well-behaved) attractive interaction always supports bound state(s). The effects of spin scattering and the spin-orbit interaction caused by $e\ensuremath{-}\mathrm{h}$ exchange are also clarified, and the DT line shape at the exciton and trion resonance is studied as a function of $e\ensuremath{-}\mathrm{h}$ exchange strength. In particular, as the exciton line shape is determined by the interplay of linear exciton susceptibility and the bound-state two-exciton resonance in the $T$ matrix, the line shape at the trion is similarly determined by the interplay of the linear trion susceptibility and the bound-state exciton-trion resonance in the $T$ matrix.

Observations of existence and instability dynamics of near-zero-dispersion temporal Kerr cavity solitons

Dissipative Kerr cavity solitons (CSs) are persisting pulses of light that manifest themselves in driven optical resonators and that have attracted significant attention over the last decade. Whilst the vast majority of studies have revolved around conditions where the resonator exhibits strong anomalous dispersion, recent studies have shown that solitons with unique characteristics and dynamics can arise under conditions of near-zero-dispersion driving. Here, we report on experimental studies of the existence and stability dynamics of Kerr CSs under such conditions. In particular, we experimentally probe the solitons' range of existence and examine how their breathing instabilities are modified when group-velocity dispersion is close to zero, such that higher-order dispersion terms play a significant role. On the one hand, our experiments directly confirm earlier theoretical works that predict (i) breathing near-zero-dispersion solitons to emit polychromatic dispersive radiation, and (ii) that higher-order dispersion can extend the range over which the solitons are stable. On the other hand, our experiments also reveal a novel cross-over scenario, whereby the influence of higher-order dispersion changes from stabilising to destabilising. Our comprehensive experiments sample soliton dynamics both in the normal and anomalous dispersion regimes, and our results are in good agreement with numerical simulations and theoretical predictions.

Nanoprecipitation of Biocompatible Poly(malic acid) Derivative, Its Ability to Encapsulate a Molecular Photothermal Agent and Photothermal Properties of the Resulting Nanoparticles.

Biocompatible nanoparticles (NPs) of hydrophobic poly(benzyl malate) (PMLABe) were prepared by nanoprecipitation. The influence of nanoprecipitation parameters (initial PMLABe, addition rate, organic solvent/water ratio and stirring speed) were studied to optimize the resulting formulations in terms of hydrodynamic diameter (Dh) and dispersity (PDI). PMLABe NPs with a Dh of 160 nm and a PDI of 0.11 were isolated using the optimized nanoprecipitation conditions. A hydrophobic near infra-red (NIR) photothermally active nickel-bis(dithiolene) complex (Ni8C12) was then encapsulated into PMLABe NPs using the optimized nanoprecipitation conditions. The size and encapsulation efficiency of the NPs were measured, revealing that up to 50 weight percent (wt%) of Ni8C12 complex can efficiently be encapsulated with a slight increase in Dh of the corresponding Ni8C12-loaded NPs. Moreover, we have shown that NP encapsulating Ni8C12 were stable under storage conditions (4 °C) for at least 10 days. Finally, the photothermal properties of Ni8C12-loaded NPs were evaluated and a high photothermal efficiency (62.7 ± 6.0%) waswas measured with NPs incorporating 10 wt% of the Ni8C12 complex.

Urban road greenbelt configuration: The perspective of PM2.5 removal and air quality regulation.

The establishment of the road green belt (RGB) is an effective means to reduce particle matter (PM2.5) emissions from road traffic. This study tested the ability of 23 common tree species in Shenzhen to reduce PM2.5 concentrations using field investigations and wind tunnel tests. The association between leaf microstructure and individual reduction ability was also analyzed. Finally, the impact of three RGB configurations (i.e., arbor, shrub, arbor+shrub) on road PM2.5 dispersion and deposition was simulated using the ENVI-met three-dimensional aerodynamic model, based on which an optimal RGB configuration was proposed. There were three key findings of the tests. First, the wind speed was the main factor affecting the PM2.5 concentration (54.2%), followed by vehicle flow (27.7%), temperature (14.2%), and time factor (7.6%). Second, the range of dry deposition velocity (Vd) was 0.04-6.4m/s, and the dominant dust-retaining plant species were the evergreen trees, Ficus microcarpa and Ficus altissima, and the evergreen shrubs, Codiaeum variegatum and Fagraea ceilanica. A higher proportion of grooves or larger stomata would increase the probability that the blade would capture PM2.5. Third, the shrub RGB demonstrated the best performance in terms of pollutant dispersion; its PM2.5 concentration at the respiratory height (RH, 1.5m) on the pedestrian crossing was 15-20% lower than the other RGB configurations. In terms of pollutant deposition, the arbor+shrub composite RGB was two-fold better than the other RGB configurations. Moreover, it was more advantageous to plant shrub RGBs in street canyons to achieve a balance between the lowest concentration and the largest deposition of PM2.5 pollutants. The findings of this study will facilitate the RGB configurations with good dust retention ability.

Temperature influence on the formation of triangular features superimposed on nanoripples produced by low-energy ion beam

Low energy ion beam-induced nanoscale ripple patterns have attracted attention due to their use in various technological applications. Making defect free, highly regular, and low wavelength (∼30 nm) ripple patterns is still under investigation as ripple patterns form over triangular features (elevations and depressions) that curtail their use in an application. In this work using 300 eV Ar+ ion beam, the topographic evolution of such triangular features at elevated temperature up to 500 °C for ion fluences of 2 × 1018 to 1 × 1019 ions cm−2 was examined. Triangular features remain intact well up to 200 °C with a marginal decrease in the base angle. Above 300 °C, triangular features start corrugating and, finally both triangular features and ripple vanished at 500 °C. The experimental findings were compared using modified anisotropic Kuramoto-Sivanshinsky (AKS) equation by Loew and Bradley (LB) incorporating simultaneously diffusion coefficient and third order dispersion term. Temperature-induced effects are adequately replicated; dispersion produces the triangular features and diffusion helps to grow it further. In experiment base angle and lateral length of the triangles decrease with increasing temperature, similar trend was observed in numerical simulations by varying the diffusion coefficient.

Quantification of Myocyte Disarray in Human Cardiac Tissue.

Proper three-dimensional (3D)-cardiomyocyte orientation is important for an effective tension production in cardiac muscle. Cardiac diseases can cause severe remodeling processes in the heart, such as cellular misalignment, that can affect both the electrical and mechanical functions of the organ. To date, a proven methodology to map and quantify myocytes disarray in massive samples is missing. In this study, we present an experimental pipeline to reconstruct and analyze the 3D cardiomyocyte architecture in massive samples. We employed tissue clearing, staining, and advanced microscopy techniques to detect sarcomeres in relatively large human myocardial strips with micrometric resolution. Z-bands periodicity was exploited in a frequency analysis approach to extract the 3D myofilament orientation, providing an orientation map used to characterize the tissue organization at different spatial scales. As a proof-of-principle, we applied the proposed method to healthy and pathologically remodeled human cardiac tissue strips. Preliminary results suggest the reliability of the method: strips from a healthy donor are characterized by a well-organized tissue, where the local disarray is log-normally distributed and slightly depends on the spatial scale of analysis; on the contrary, pathological strips show pronounced tissue disorganization, characterized by local disarray significantly dependent on the spatial scale of analysis. A virtual sample generator is developed to link this multi-scale disarray analysis with the underlying cellular architecture. This approach allowed us to quantitatively assess tissue organization in terms of 3D myocyte angular dispersion and may pave the way for developing novel predictive models based on structural data at cellular resolution.

Improvement of the Gaussian Electrostatic Model by separate fitting of Coulomb and exchange-repulsion densities and implementation of a new dispersion term.

The description of each separable contribution of the intermolecular interaction is a useful approach to develop polarizable force fields (polFFs). The Gaussian Electrostatic Model (GEM) is based on this approach, coupled with the use of density fitting techniques. In this work, we present the implementation and testing of two improvements of GEM: the Coulomb and exchange-repulsion energies are now computed with separate frozen molecular densities and a new dispersion formulation inspired by the Sum of Interactions Between Fragments Ab initio Computed polFF, which has been implemented to describe the dispersion and charge-transfer interactions. Thanks to the combination of GEM characteristics and these new features, we demonstrate a better agreement of the computed structural and condensed properties for water with experimental results, as well as binding energies in the gas phase with the ab initio reference compared with the previous GEM* potential. This work provides further improvements to GEM and the items that remain to be improved and the importance of the accurate reproduction for each separate contribution.

Spatiotemporal couplings through a nonlinear phase in broadband optical parametric amplification.

Optical parametric chirped-pulse amplification (OPCPA) is prone to undesired spatiotemporal couplings. This Letter studies a family of OPCPA couplings resulting from the nonlinear phase shift induced by frequency-dependent phase mismatch. These OPCPA couplings manifest as pulse-front deformation, transversely varying pulse duration, and spectrally varying wavefront curvature, which are directly linked with the phase-mismatch dispersion terms. The numerical study in this Letter also reveals that the focused signal intensity severely degrades with increasing signal bandwidth and pump depletion.

On the Gaussian traveling wave solution to a special kind of Schrödinger equation with logarithmic nonlinearity

We present the complete analysis of traveling wave solutions to a special kind of nonlinear Schrödinger equation with logarithmic nonlinearity, and obtain all traveling wave solutions. As a result, we prove this equation does not have any Gaussian traveling wave solution. However, by modifying this equation into another form, we can actually obtain a Gaussian traveling wave solution, which verifies the conclusion that existing Gaussian traveling solution requires two restrictions: (1) balance between the dispersion terms and logarithmic nonlinearity; and (2) balance of the parameters.

A Combined Experimental/Quantum-Chemical Study of Tetrel, Pnictogen, and Chalcogen Bonds of Linear Triatomic Molecules.

Linear triatomic molecules (CO2, N2O, and OCS) are scrutinized for their propensity to form perpendicular tetrel (CO2 and OCS) or pnictogen (N2O) bonds with Lewis bases (dimethyl ether and trimethyl amine) as compared with their tendency to form end-on chalcogen bonds. Comparison of the IR spectra of the complexes with the corresponding monomers in cryogenic solutions in liquid argon enables to determine the stoichiometry and the nature of the complexes. In the present cases, perpendicular tetrel and pnictogen 1:1 complexes are identified mainly on the basis of the lifting of the degenerate ν 2 bending mode with the appearance of both a blue and a red shift. Van ′t Hoff plots of equilibrium constants as a function of temperature lead to complexation enthalpies that, when converted to complexation energies, form the first series of experimental complexation energies on sp1 tetrel bonds in the literature, directly comparable to quantum-chemically obtained values. Their order of magnitude corresponds with what can be expected on the basis of experimental work on halogen and chalcogen bonds and previous computational work on tetrel bonds. Both the order of magnitude and sequence are in fair agreement with both CCSD(T) and DFA calculations, certainly when taking into account the small differences in complexation energies of the different complexes (often not more than a few kJ mol−1) and the experimental error. It should, however, be noted that the OCS chalcogen complexes are not identified experimentally, most probably owing to entropic effects. For a given Lewis base, the stability sequence of the complexes is first successfully interpreted via a classical electrostatic quadrupole–dipole moment model, highlighting the importance of the magnitude and sign of the quadrupole moment of the Lewis acid. This approach is validated by a subsequent analysis of the molecular electrostatic potential, scrutinizing the σ and π holes, as well as the evolution in preference for chalcogen versus tetrel bonds when passing to “higher” chalcogens in agreement with the evolution of the quadrupole moment. The energy decomposition analysis gives further support to the importance/dominance of electrostatic effects, as it turns out to be the largest attractive term in all cases considered, followed by the orbital interaction and the dispersion term. The natural orbitals for chemical valence highlight the sequence of charge transfer in the orbital interaction term, which is dominated by an electron-donating effect of the N or O lone-pair(s) of the base to the central atom of the triatomics, with its value being lower than in the case of comparable halogen bonding situations. The effect is appreciably larger for TMA, in line with its much higher basicity than DME, explaining the comparable complexation energies for DME and TMA despite the much larger dipole moment for DME.

Remarks on the Boundary Conditions for a Serre-Type Model Extended to Intermediate-Waters

Numerical models are useful tools for studying complex wave–wave and wave–current interactions in coastal areas. They are also very useful for assessing the potential risks of flooding, hydrodynamic actions on coastal protection structures, bathymetric changes along the coast, and scour phenomena on structures’ foundations. In the coastal zone, there are shallow-water conditions where several nonlinear processes occur. These processes change the flow patterns and interact with the moving bottom. Only fully nonlinear models with the addition of dispersive terms have the potential to reproduce all phenomena with sufficient accuracy. The Boussinesq and Serre models have such characteristics. However, both standard versions of these models are weakly dispersive, being restricted to shallow-water conditions. The need to extend them to deeper waters has given rise to several works that, essentially, add more or fewer terms of dispersive origin. This approach is followed here, giving rise to a set of extended Serre equations up to kh ≈ π. Based on the wavemaker theory, it is also shown that for kh > π/10, the input boundary condition obtained for shallow-waters within the Airy wave theory for 2D waves is not valid. A better estimate for the input wave that satisfies a desired value of kh can be obtained considering a geometrical modification of the conventional shape of the classic piston wavemaker by a limited depth θh, with θ≤ 1.0.

Tuning single-walled aligned carbon nanotubes for optimal terahertz pulse generation through optical rectification of ultrashort laser pulses.

Terahertz radiation by optical rectification in single-walled highly aligned chiral carbon nanotubes (SWCNTs) irradiated by ultrashort laser pulses is comprehensively studied. We take into account the structural properties of SWCNTs, including the filling factor, alignment, and chirality, as well as the laser pulse parameters including the pulse duration and the wavelength. The second-order nonlinear susceptibility tensor and, consequently, polarization responsible for optical rectification in SWCNTs are derived based on symmetrical features.The effective dielectric constants of SWCNTs are also extracted using the effective medium approximation. Then, the propagation effects in terms of the group velocity dispersion and absorption at both pump and terahertz pulse frequency regions are investigated. By adjusting the laser and the structure effective parameters among those practically feasible, minimum velocity mismatch required for optimum optical rectification and coherent amplification at terahertz frequencies in SWCNTs are introduced. Comparing the electric field waveform and the spectrum of the generated terahertz pulses under various conditions reveals that SWCNTs with higher alignment and lower filling factor at chirality (6,4) irradiated by an ultrashort laser pulse with the wavelength of 1550 nm could provide the conditions for maximum terahertz radiation generation.

Chemical composition, functional and technological (processing) properties of whey ingredients

The growth in volumes of the milk whey manufacturing has revealed the new field of processing, such as dry whey ingredients production. The authors have made investigations of chemical composition, functional and technological (processing) properties of whey protein concentrates with protein of 35, 55, 80 % in dry matter, whey protein hydrolysate and cheese whey permeate. We used standard methods, generally accepted in research practice. The chemical composition of the tested samples has been determined, including their rehydration properties in terms of wettability, dispersibility and solubility. Heat denaturation of whey proteins during the processing is the reason for the bound groups–SH release and their reactivity enhancement, which provides antioxidant effect of whey ingredients (the antioxidant content in the tested samples is 0.031; 0.058; 0.095; 0.146 and 0.024 mg/g for the whey protein concentrates with protein of 35, 55, 80 % in dry matter, whey protein hydrolysate and whey permeate respectively). The functional and technological properties of whey ingredients make possible their application while producing different product line groups in order to control the technological processes and the quality factors of the enriched products.

Identification of Fe-Zn coating behaviors by a new reverse approach using artificial intelligence

Nanoindentation is a technique commonly used to measure the mechanical properties of thin films even at depths less than 1 μm. In fact, the characterization is based on the study of the load/displacement curves resulting from the nanoindentation test. We aim to use the backtracking search optimization algorithm (BSA) to improve the extraction of P(h) curves performed by nanoindentation on galvannealed Fe-Zn coating in terms of precision and dispersion. Indeed, the originality of this study is not limited only to the P(h) curve extraction methods, but also to its application in modeling the reverse approach for the case of Fe-Zn coating deposited on a Dual-Phase DP600 steel substrate. Indeed, the BSA approach showed more precision (with respect to the determined mean value) and less dispersion (magnitude of error around the identified mean value) compared to the Least-squares approach. The average error with the BSA and LS methods is respectively 0.89% and 3.16% for the yield stress and 3.17% and 7.93% for the strain hardening exponent (n). This reduced the error variability in the prediction of the constitutive law to 72% and 60% for () and n, respectively. Thus, we solved the problems of accessibility, uniqueness of the solution, precision (+10%) and dispersion (−85%) of the required prediction models for the Fe-Zn coating behavior.

Design of Ultra-Compact On-Chip Discrete Phase Filters for Broadband Dispersion Management

This paper provides an in-depth theoretical and numerical analysis of a group-velocity dispersion (GVD) management scheme for broadband waveforms using ultra-compact on-chip discrete spectral phase filters based upon waveguide Bragg gratings (WBGs) in a silicon-on-insulator (SOI) platform. Through this technique, mm-long discrete phase filters can be designed to impart a target arbitrary GVD profile on a high-rate (typically, $\geq\!10$ GHz) periodic pulsed waveform, including fully customized and extremely large second and higher-order dispersion terms (e.g., equivalent to 10,000 km of a standard single-mode fiber), over a broad frequency bandwidth (up to $\sim\!3$ THz, demonstrated here). The capabilities and limitations of this technique to impart a target GVD profile over an arbitrary (generally, non-periodic) broadband signal are also studied. We show that customized GVD lines can be efficiently implemented offering a net group-delay excursion in the hundreds-of-ps range using mm-long integrated discrete phase filters. Additionally, we suggest and numerically demonstrate a simple and practical strategy to improve significantly the performance of the discrete phase filtering approach for application on non-periodic waveforms, by combining the discrete phase filter with a suitable periodic resonance (frequency-comb) amplitude filter. An extensive tolerance analysis is conducted, and we conclude that the proposed SOI design framework is well within practical fabrication requirements as well as robust to the expected variability in the main WBG device design parameters.

Higher-dimensional extended shallow water equations and resonant soliton radiation

Higher order equations governing long surface waves in shallow water beyond the standard Korteweg-de Vries and Kadomtsev-Petviashvili equations are derived from the full water wave equations. The higher order dispersive and nonlinear terms in these equations lead to resonance between nonlinear wave structures and dispersive radiation. This resonance between solitary waves and dispersive shock waves (undular bores) is studied numerically and analytically using exponential asymptotic theory. A key result is that there is a near node in the resonant wave amplitude for the higher order equations with the water wave coefficients.

Full-Dimensional Potential Energy Surface for Ro-vibrationally Inelastic Scattering between H2 Molecules.

We report a new full-dimensional potential energy surface (PES) for the inelastic scattering between ro-vibrationally excited H2 molecules. The new PES is based on 39,462 multi-reference configuration interaction points in dynamically relevant regions. The analytic form of the PES consists of a short-range term fit with the permutational invariant polynomial-neural network method and a long-range term with a physically correct asymptotic functional form accounting for both electrostatic and dispersion terms, which are connected smoothly with a switching function. The PES compares favorably with existing accurate PESs near the H2 equilibrium geometries but covers a much larger configuration space for H2 with up to 10 vibrational quanta. Full-dimensional quantum scattering calculations on the new PES reproduce the recent Stark-induced adiabatic Raman passage results for the HD(v = 1) + H2 scattering near 1 K, validating its accuracy. These calculations also revealed significant differences with existing PESs in describing scattering of vibrationally excited molecules, underscoring the ability of the new PES in handling such dynamics.

Soliton interaction of a generalized nonlinear Schrödinger equation in an optical fiber

Under investigation in this work is a generalized nonlinear Schrödinger (NLS) equation with high-order dispersion and quintic nonlinear terms, which can describe a subpicosecond pulse propagation in optical fibers. By developing Hirota method, the bilinear form and analytical one- and two-soliton solutions are derived. Based on the analytical solutions, we give the corresponding soliton patterns to analyse dynamics of the pulse solitons. It shows that high order dispersion term may change the periodicity of propagation. The interaction of two pulse solitons is an elastic collision. By choosing suitable parameter values, we can obtain the two parallel solitons. It can be applied to improve transmission quality and capacity of information in optical fiber.

Asymptotic behavior of solution of Whitham–Broer–Kaup type equations with negative dispersion

Abstract In this work, we discuss the long time behavior of solutions of the Whitham–Broer–Kaup system with Lipschitz nonlinearity and negative dispersion term. We prove the global well-posedness when α + β 2 < 0 {\alpha+\beta^{2}<0} as well as the convergence to 0 of small solutions at rate 𝒪 ⁢ ( t - 1 / 2 ) {\mathcal{O}(t^{-1/2})} .

Unraveling the Link between Catalytic Activity and Agglomeration State with SECM and AFM

Scanning electrochemical microscopy (SECM) is at the forefront of a new generation of tools enabling to investigate the local properties of catalysts [1]. Thanks to its ability to study a very low amount of material with almost no additives such as a polymeric binder (Nafion), the intrinsic activity of catalysts gets accessible and characterizations can be performed at agglomerate scale. Herein, we propose to combine for the first time SECM with atomic force microscopy (AFM) characterizations to study the link between the catalytic activity and the agglomeration state of non-PGM (platinum group metal) ORR catalysts. SECM is performed with the redox competition mode in acidic media, following the protocol developed recently in our group [2]. AFM images are then used to determine the agglomeration state in the deposits of catalysts.Two PGM-free ORR catalysts were investigated at different loadings [3]. Differences in term of dispersion, stability of the inks and adherence on the substrate were observed, which highlights the importance of measuring the exact amount and agglomeration state of the material deposited. The agglomeration states of the deposits measured by AFM enabled to explain the differences in activity measured by SECM. The performances of the catalysts were compared and the contributions of the intrinsic activity and the agglomeration state were separated. These results illustrate that our approach is suitable for the characterization of catalysts at agglomerate scale, with various applications from the benchmarking of new catalysts to the optimization of an ink formulation.