Solitonic dispersive hydrodynamics: theory and observation

Ubiquitous nonlinear waves in dispersive media include localized solitons and extended hydrodynamic states such as dispersive shock waves. Despite their physical prominence and the development of thorough theoretical and experimental investigations of each separately, experiments and a unified theory of solitons and dispersive hydrodynamics are lacking. Here, a general soliton-mean field theory is introduced and used to describe the propagation of solitons in macroscopic hydrodynamic flows. Two universal adiabatic invariants of motion are identified that predict trapping or transmission of solitons by hydrodynamic states. The result of solitons incident upon smooth expansion waves or compressive, rapidly oscillating dispersive shock waves is the same, an effect termed hydrodynamic reciprocity. Experiments on viscous fluid conduits quantitatively confirm the soliton-mean field theory with broader implications for nonlinear optics, superfluids, geophysical fluids, and other dispersive hydrodynamic media.Comment: 8 pages, 5 figure

Solitary wave fission of a large disturbance in a viscous fluid conduit

This paper presents a theoretical and experimental study of the long-standing fluid mechanics problem involving the temporal resolution of a large localised initial disturbance into a sequence of solitary waves. This problem is of fundamental importance in a range of applications, including tsunami and internal ocean wave modelling. This study is performed in the context of the viscous fluid conduit system – the driven, cylindrical, free interface between two miscible Stokes fluids with high viscosity contrast. Owing to buoyancy-induced nonlinear self-steepening balanced by stress-induced interfacial dispersion, the disturbance evolves into a slowly modulated wavetrain and further into a sequence of solitary waves. An extension of Whitham modulation theory, termed the solitary wave resolution method, is used to resolve the fission of an initial disturbance into solitary waves. The developed theory predicts the relationship between the initial disturbance’s profile, the number of emergent solitary waves and their amplitude distribution, quantifying an extension of the well-known soliton resolution conjecture from integrable systems to non-integrable systems that often provide a more accurate modelling of physical systems. The theoretical predictions for the fluid conduit system are confirmed both numerically and experimentally. The number of observed solitary waves is consistently within one to two waves of the prediction, and the amplitude distribution shows remarkable agreement. Universal properties of solitary wave fission in other fluid dynamics problems are identified

Novel Magnetic and Optical Properties of Sn\u3csub\u3e1−x\u3c/sub\u3eZn\u3csub\u3ex\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3e Nanoparticles

In this work, we report on the effects of doping SnO2 nanoparticles with Zn2+ ions. A series of ∼2–3 nm sized Sn1−x ZnxO2 crystallite samples with 0 ≤ x ≤ 0.18 were synthesized using a forced hydrolysis method. Increasing dopant concentration caused systematic changes in the crystallite size, oxidation state of Sn, visible emission, and band gap of SnO2 nanoparticles. X-ray Diffraction studies confirmed the SnO2 phase purity and the absence of any impurity phases. Magnetic measurements at room temperature showed a weak ferromagnetic behavior characterized by an open hysteresis loop. Their saturation magnetization Ms increases initially with increasing Zn concentrations; however for x \u3e 0.06, Ms decreases. Samples with the highest Ms values (x = 0.06) were analyzed using an Inductively Coupled Plasma Mass Spectrometer, looking for traces of any magnetic elements in the samples. Concentrations of all transition metals (Fe, Co, Mn, Cr, and Ni) in these samples were below ppb level, suggesting that the observed magnetism is not due to random inclusions of any spurious magnetic impurities and it cannot be explained by the existing models of magnetic exchange. A new visible emission near 490 nm appeared in the Zn doped SnO2 samples in the photoluminescence spectra which strengthened as x increased, suggesting the formation of defects such as oxygen vacancies. X-ray Photoelectron Spectroscopy (XPS) confirmed the nominal Zn dopant concentrations and the 2+ oxidation state of Zn in the Sn1−x ZnxO2 samples. Interestingly, the XPS data indicated the presence of a small fraction of Sn2+ ions in Sn1−xZnxO2 samples in addition to the expected Sn4+, and the Sn2+ concentration increased with increasing x. The presence of multi-valent metal ions and oxygen defects in high surface area oxide nanoparticles has been proposed as a potential recipe for weak ferromagnetis

Dopant Spin States and Magnetism of Sn\u3csub\u3e1−x\u3c/sub\u3eFe\u3csub\u3ex\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3e Nanoparticles

This work reports detailed investigations of a series of ∼2.6 nm sized, Sn1−xFexO2 crystallites with x = 0–0.10 using Mossbauer spectroscopy, x-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR), and magnetometry to determine the oxidation state of Fe dopants and their role in the observed magnetic properties. The magnetic moment per Fe ion μ was the largest ∼6.48 × 10−3 μB for the sample with the lowest (0.001%) Fe doping, and it showed a rapid downward trend with increasing Fe doping. Majority of the Fe ions are in 3+ oxidation state occupying octahedral sites. Another significant fraction of Fe dopant ions is in 4+ oxidation state and a still smaller fraction might be existing as Fe2+ ions, both occupying distorted sites, presumably in the surface regions of the nanocrystals, near oxygen vacancies. These studies also suggest that the observed magnetism is not due to exchange coupling between Fe3+ spins. A more probable role for the multi-valent Fe ions may be to act as charge reservoirs, leading to charge transfer ferromagnetism

Novel and Magnetic Properties of Sn1-xZnxO2 Nanoparticles

In this work, we report on the effects of doping SnO2 nanoparticles with Zn2+ ions. A series of ~2- 3nm sized Sn1-xZnxO2 crystallite samples with 0 ≤ x ≤ 0.18 were synthesized using a forced hydrolysis method. Increasing dopant concentration caused systematic changes in the crystallite size, oxidation state of Sn, visible emission and band gap of SnO2 nanoparticles. X-ray Diffraction (XRD) studies confirmed the SnO2 phase purity and the absence of any impurity phases. Magnetic measurements at room temperature showed a weak ferromagnetic behavior characterized by an open hysteresis loop. Their saturation magnetization Ms increases initially with increasing Zn concentrations, however for x \u3e 0.06, Ms decreases. Samples with the highest Ms values (x = 0.06) were analyzed using an Inductively Coupled Plasma Mass Spectrometer (ICP-MS), looking for traces of any magnetic elements in the samples. Concentrations of all transition metals (Fe, Co, Mn, Cr, Ni) in these samples were below ppb level, suggesting the observed magnetism is not due to random inclusions of any spurious magnetic impurities and it cannot be explained by the existing models of magnetic exchange. A new visible emission near 490nm appeared in the Zn doped SnO2 samples in the photoluminescence (PL) spectra which strengthened as x increased, suggesting the formation of defects such as oxygen vacancies. X-ray Photoelectron Spectroscopy (XPS) confirmed the nominal Zn dopant concentrations and the 2+ oxidation state of Zn in the Sn1-xZnxO2 samples. Interestingly, the XPS data indicated the presence of a small fraction of Sn2+ions in Sn1- xZnxO2 samples in addition to the expected Sn4+ , and the Sn2+ concentration increased with increasing x. The presence of multi-valent metal ions and oxygen defects in high surface area oxide nanoparticles have been proposed as a potential recipe for weak ferromagnetism1. Reference: 1. J. M. D. Coey, P. Stamenov, R. D. Gunning, M. Venkatesan, and K. Paul, New Journal of Physics 12 (2010)

Zno Nanoparticle Preparation Route Influences Surface Reactivity, Dissolution and Cytotoxicity

ZnO nanoparticles (nZnO) are commonly used in nanotechnology applications despite their demonstrated cytotoxicity against multiple cell types. This underscores the significant need to determine the physicochemical properties that influence nZnO cytotoxicity. In this study, we analyzed six similarly sized nZnO formulations, along with SiO2-coated nZnO, bulk ZnO and ZnSO4 as controls. Four of the nZnO samples were synthesized using various wet chemical methods, while three employed high-temperature flame spray pyrolysis (FSP) techniques. X-ray diffraction and optical analysis demonstrated the lattice parameters and electron band gap of the seven nZnO formulations were similar. However, zeta potential measures, hydrodynamic size, photocatalytic rate constants, dissolution potential, reactive oxygen species (ROS) production and, more importantly, the cytotoxicity of the variously synthesized nZnO towards Jurkat leukemic and primary CD4+ T cells displayed major differences. Surface structure analysis using FTIR, X-ray photoelectron spectroscopies (XPS) and dynamic light scattering (DLS) revealed significant differences in the surface-bound chemical groups and the agglomeration tendencies of the samples. The wet chemical nZnO, with higher cationic surface charge, faster photocatalytic rates, increased extracellular dissolution and ROS generation demonstrated greater cytotoxicity towards both cell types than those made with FSP techniques. Furthermore, principal component analysis (PCA) suggests that the synthesis procedure employed influences which physicochemical properties contribute more to the cytotoxic response. These results suggest that the synthesis approach results in unique surface chemistries and can be a determinant of cellular cytotoxicity and oxidative stress responses