Non-homogeneous Field Research Articles

Beyond CarbonK-Edge Harmonic Emission Using a Spatial and Temporal Synthesized Laser Field

We present numerical simulations of high-order harmonic generation in helium using a temporally synthesized and spatially nonhomogeneous strong laser field. The combination of temporal and spatial laser field synthesis results in a dramatic cutoff extension far beyond the usual semiclassical limit. Our predictions are based on the convergence of three complementary approaches: resolution of the three dimensional time dependent Schrödinger equation, time-frequency analysis of the resulting dipole moment, and classical trajectory extraction. A laser field synthesized both spatially and temporally has been proven capable of generating coherent extreme ultraviolet photons beyond the carbon K edge, an energy region of high interest as it can be used to initiate inner-shell dynamics and study time-resolved intramolecular attosecond spectroscopy.

Numerical analysis of Nd:YAG pulsed laser polishing CVD self-standing diamond film

Chemical vapor deposited (CVD) diamond film has broad application foreground in high-tech fields. But polycrystalline CVD self-standing diamond thick film has rough surface and non-uniform thickness that adversely affect its extensive applications. Laser polishing is a useful method to smooth self-standing diamond film. At present, attentions have been focused on experimental research on laser polishing, but the revealing of theoretical model and the forecast of polishing process are vacant. The paper presents a finite element model to simulate and analyze the mechanism of laser polishing diamond based on laser thermal conduction theory. The experimental investigation is also carried out on Nd:YAG pulsed laser smoothing diamond thick film. The simulation results have good accordance with the results of experimental results. The temperature and thermal stress fields are investigated at different incidence angles and parameters of Nd:YAG pulsed laser. The pyramidal-like roughness of diamond thick film leads to the non-homogeneous temperature fields. The temperature at the peak of diamond film is much higher than that in the valley, which leads to the smoothing of diamond thick film. The effect of laser parameters on the surface roughness and thickness of graphite transition layer is also carried out. The results show that high power density laser makes the diamond surface rapid heating, evaporation and sublimation after its graphitization. It is also found that the good polish quality of diamond thick film can be obtained by a combination of large incident angle, moderate laser pulsed energy, large repetition rate and moderate laser pulse width. The results obtained here provide the theoretical basis for laser polishing diamond film with high efficiency and high quality.

A meshfree-Galerkin method in modelling and synthesizing spatially varying soil properties

Physical properties of soil vary from point to point in space and exhibit great uncertainty, suggesting random field as a natural approach in modelling and synthesizing these properties. The significance of considering spatial variability and uncertainty of soil properties is greatly manifested in the probabilistic seismic risk analysis of soil–structural system (nonlinear dynamic analysis under earthquake loading), where modelling and synthesis of the spatial variability and uncertainty of soil properties are necessary. This paper introduces a meshfree-Galerkin approach within the Karhunen–Loève (K–L) expansion scheme for representation of spatial soil properties modelled as the random fields. The meshfree shape functions are introduced and employed as a set of basis functions in the Galerkin scheme to obtain the eigen-solutions of integral equation of K–L expansion. An optimization scheme is proposed for the resulting eigenvectors in treating the compatibility between the target and analytical covariance models. Assessments of the meshfree-Galerkin method are conducted for the resulting eigen-solutions and the representation of covariance models for various homogeneous and nonhomogeneous random fields. The accuracy and validity of the proposed approach are demonstrated through the modelling and synthesis of the spatial field models inferred from the field measurements.

The contribution of space charge in a high non-homogenous electric field to the creation of negative differential conductivity

The paper describes anomaly origination on current or voltage characteristics in time of positive potential on small curvature radius electrode rod against plane electrodes. An anomaly phenomenon occurred in the narrow voltage area in a high non-homogenous electric field close to the electrode ( E > 10 7 V m −1 ). A mathematical – physical analysis of the observed processes in close proximity to the electrode with the above mentioned form is made. The differential equations, which analytically and theoretically describe this phenomenon, are compiled and solved. The space charge created by element particles (electrons, ions) which causes negative differential conductivity origination in narrow voltage area by their behaviour in electric field, plays a substantial role in this phenomenon. Current–voltage characteristics at both polarities of corona electrode were continuously measured at the study of static and dynamic processes occurring during discharge in the surrounding of a small curvature radius electrode. It was proved that an anomaly, in the form of negative differential conductivity ( dI / dU < 0), appeared on a highly curved electrode at positive polarity in a narrow voltage area. This phenomenon was subjected to detailed experimental research including investigation of the influence of the shape and material of the electrode (output voltage), electrode temperature, influence of photoionization on the profile of the anomaly, the contribution of exoelectrons to particle distribution, and study of electrochemical potential of metal electrode. Oscillation of low ionized plasma at positive and negative polarity of small curvature radius electrodes has been analyzed. At the same time, the influence of the external forced electric field on the change of current–voltage characteristic profile was investigated. Theoretical justification of the anomaly phenomenon resulted from a change of energy conditions in the investigated place (the distance limit from the electrode is 10 −4 –10 −6 m).

Magnetic fluid in ionizing electric field

Abstract This article describes influence of strong (ionizing) electric field on sprayability of magnetic fluid containing colloid particles with size in the range from 10 to 20 nm of magnetite Fe 3 O 4 . Magnetic fluids can be based for example on both transformer oil and physiological solution for application in medical using (in human medical science research), that supports a fluid colloidal system. Further component of magnetic fluid is surfactant. It is acting as surface-active substance that prevents from nanometric dimension particle settlement. Magnetic fluid gets off nozzle with diameter in range 0.3–1.0 mm from container in surroundings of ionizing (i.e. strong) electric field ( E > 10 7 V m −1 ). As a consequence of action of electric field it gives out suppression surface tension in fluid what leads onwards to decomposition of magnetic fluid ligament at the end of nozzle. The diameter of nozzle oneself respects basic theoretical calculations in regards of fluid concentration and thereinbefore its selected size. Magnetic fluid in dependency on its used liquid base has weak-polar till polar orientation polarization character. It gives out sprayability in non-homogeneous electric field E in combination with magnetic field of intensity H . Orientation of vectors E and Ĥ , resp. induction of magnetic field B is defined by parallel or vertical direction. Results are confronted with measurements realized explicitly only at action of electric field (variable B = 0). In the case of magnetic field applications with permanent magnet together with electric non-homogeneous field it gives out unconventional dynamics of electrical charging particles of macroscopic dimension. Orientation particle track is influenced by orientation of field vector combinations. This phenomenon develops magneto-dielectric anisotropy, which oneself manifests behaviour of electrophysical quantities characterizing examination system. In consideration of technology utilization of this method it is very important to respect applied magnetic fluid concentration. Electrical characteristics were examined for volume concentration of magnetite particles in the range from 0.125% to 18%. Nevertheless efficiency optimization of given media suggests to boundary concentration of magnetic fluid of 4.0%, when it is in the regions of weak polar till polar material. Electrophysical research refers to exploitation of applied magnetic layer technology on dielectric insulating substances with inorganic origin as well as thin layer technology coating plastic foils created from macromolecular organic substance.

NONLINEAR WAVE PRESSURES GIVEN BY EXTREME WAVES ON AN UPRIGHT BREAKWATER: THEORY AND EXPERIMENTAL VALIDATION

An analytical nonlinear theory is presented for the interaction between three-dimensional sea wave groups and a seawall during the occurrence of an exceptionally high crest or deep trough of the water elevation. The solution to the second order of the free surface displacement and of the velocity potential is derived by considering an irrotational, inviscid, incompressible flow bounded by a horizontal seabed and a vertical impermeable seawall. The analytical expression of the nonlinear wave pressure is derived. The resulting theory is able to fully describe the mechanics at the seawall and in front of it, which represents a strongly nonhomogeneous wave field, then demonstrating that it is influenced by characteristic parameters and wave conditions. The theoretical results are in good agreement with measurements carried out during a small-scale field experiment at the Natural Ocean Engineering Laboratory in Reggio Calabria (Italy). The theoretical and experimental comparisons show that some distinctive phenomena regarding wave pressures of very high standing wave groups at a seawall, in the absence of either overturning or breaking waves, may be associated with nonlinear effects.

Buckling analysis of I-section portal frames with stochastic imperfections

This work examines the effect of random geometric imperfections in the buckling response of I-profile steel beam–column members as well as portal frame structures. Geometric imperfections are assumed to be non-homogeneous Gaussian random fields. Samples of these fields are generated using the spectral representation method with evolutionary power spectra derived from experimental measurements using the method of separation. A number of samples of random imperfect geometries are generated and simulated with detailed discretization with triangular shell finite elements. The stochastic buckling loads are determined in the context of brute force Monte Carlo simulation by repeated material and geometrically nonlinear finite element analyses. Single beam–column members are subjected to pure axial compression while the portal frames are tested for lateral loading. Various types of boundary conditions are implemented and histograms of bucking loads are derived for each case examined leading to useful conclusions for this type of structures, regarding imperfection triggered buckling response and buckling load variability.

Ab initiocontinuum model for the influence of local stress on cross-slip of screw dislocations in fcc metals

We develop a model of cross-slip in face-centered cubic (fcc) metals based on an extension of the Peierls-Nabarro representation of the dislocation core. The dissociated core is described by a group of parametric fractional Volterra dislocations, subject to their mutual elastic interaction and a lattice-restoring force. The elastic interaction between them is computed from a nonsingular expression, while the lattice force is derived from the $\ensuremath{\gamma}$ surface obtained directly from ab initio calculations. Using a network-based formulation of dislocation dynamics, the dislocation core structure is not restricted to be planar, and the activation energy is determined for a path where the core has three-dimensional equilibrium configurations. We show that the activation energy for cross-slip in Cu is $1.9\phantom{\rule{4pt}{0ex}}\text{eV}$ when the core is represented by only two Shockley partials, while this value converges to $1.43\phantom{\rule{4pt}{0ex}}\text{eV}$ when the core is distributed over a bundle of 20 Volterra partial fractional dislocations. The results of the model compare favorably with the experimental value of $1.15\ifmmode\pm\else\textpm\fi{}0.37\phantom{\rule{4pt}{0ex}}\text{eV}$ [J. Bonneville and B. Escaig, Acta Metall. 27, 1477 (1979)]. We also show that the cross-slip activation energy decreases significantly when the core is in a particular local stress field. Results are given for a representative uniform ``Escaig'' stress and for the nonuniform stress field at the head of a dislocation pileup. A local homogeneous stress field is found to result in a significant reduction of the cross-slip energy. Additionally, for a nonhomogeneous stress field at the head of a five-dislocation pileup compressed against a Lomer-Cottrell junction, the cross-slip energy is found to decrease to $0.62\phantom{\rule{4pt}{0ex}}\text{eV}$. The relatively low values of the activation energy in local stress fields predicted by the proposed model suggest that cross-slip events are energetically more favorable in strained fcc crystals.

Occupational exposure assessment of magnetic fields generated by induction heating equipment—the role of spatial averaging

Induction heating equipment is a source of strong and nonhomogeneous magnetic fields, which can exceed occupational reference levels. We investigated a case of an induction tempering tunnel furnace. Measurements of the emitted magnetic flux density (B) were performed during its operation and used to validate a numerical model of the furnace. This model was used to compute the values of B and the induced in situ electric field (E) for 15 different body positions relative to the source. For each body position, the computed B values were used to determine their maximum and average values, using six spatial averaging schemes (9–285 averaging points) and two averaging algorithms (arithmetic mean and quadratic mean). Maximum and average B values were compared to the ICNIRP reference level, and E values to the ICNIRP basic restriction. Our results show that in nonhomogeneous fields, the maximum B is an overly conservative predictor of overexposure, as it yields many false positives. The average B yielded fewer false positives, but as the number of averaging points increased, false negatives emerged. The most reliable averaging schemes were obtained for averaging over the torso with quadratic averaging, with no false negatives even for the maximum number of averaging points investigated.

Seebeck effect in electrolytes

We study Seebeck effect in liquid electrolytes, starting from its simple neutral analog--thermodiffusion (so-called Ludwig-Soret or Soret effect). It is observed that when two or more subsystems of mobile particles are subjected to the temperature gradient, various types of them respond to it differently. In the case when these fractions, with different mobility parameters (Soret coefficients), are oppositely charged (a case typical for electrolytes), the nonhomogeneous internal electric field is generated. The latter field prevents these fractions from space separation and determines the intensity of the appearing Seebeck effect.

Gradient-Oriented State of Polymers: Formation and Investigation

The concept of a gradient-oriented state of polymers is formulated for the first time and some regularities of the formation of this state are established. The specific influence of non-homogeneous mechanical fields is demonstrated by means of the example of the creation of gradient birefringence (GB) elements. These are the focus of research into the new non-traditional direction of gradient birefringence (GB) optics. Possible areas of application for GB elements are polarized compensators, polarized holography and photonics, the interference-polarizing GB monochromator, luminescence analysis, etc.

Experimental investigation on convective heat transfer of magnetic phase change microcapsule suspension

This paper is to conduct experimental investigation on the convective heat transfer of magnetic phase change microcapsule (MPCMC) suspension in the presence of an external non-homogenous magnetic field. The effects of the external magnetic field intensity, the volume fraction of MPCMC particles and the mass flow rate of MPCMC suspension on the convective heat transfer of MPCMC suspension are investigated. The experimental data reveal that the convective heat transfer of MPCMC suspension is significantly enhanced by the external non-homogenous magnetic field.

NIMASTEP: a software to modelize, study, and analyze the dynamics of various small objects orbiting specific bodies

NIMASTEP is a dedicated numerical software developed by us, which allows one to integrate the osculating motion (using cartesian coordinates) in a Newtonian approach of an object considered as a point-mass orbiting a homogeneous central body that rotates with a constant rate around its axis of smallest inertia. The code can be applied to objects such as particles, artificial or natural satellites or space debris. The central body can be either any terrestrial planet of the solar system, any dwarf-planet, or even an asteroid. In addition, very many perturbations can be taken into account, such as the combined third-body attraction of the Sun, the Moon, or the planets, the direct solar radiation pressure (with the central body shadow), the non-homogeneous gravitational field caused by the non-sphericity of the central body, and even some thrust forces. The simulations were performed using different integration algorithms. Two additional tools were integrated in the software package; the indicator of chaos MEGNO and the frequency analysis NAFF. NIMASTEP is designed in a flexible modular style and allows one to (de)select very many options without compromising the performance. It also allows one to easily add other possibilities of use. The code has been validated through several tests such as comparisons with numerical integrations made with other softwares or with semi-analytical and analytical studies. The various possibilities of NIMASTEP are described and explained and some tests of astrophysical interest are presented. At present, the code is proprietary but it will be released for use by the community in the near future. Information for contacting its authors and (in the near future) for obtaining the software are available on the web site http://www.fundp.ac.be/en/research/projects/page_view/10278201/

High-order-harmonic generation from inhomogeneous fields

We present theoretical studies of high-order-harmonic generation (HHG) produced by nonhomogeneous fields resulting from the illumination of plasmonic nanostructures with a short laser pulse. We show that both the inhomogeneity of the local fields and the confinement of the electron movement play an important role in the HHG process and lead to the generation of even harmonics and a significantly increased cutoff, more pronounced for the longer-wavelength cases studied. In order to understand and characterize the new HHG features, we employ two different approaches: the numerical solution of the time-dependent Schr\"odinger equation and the semiclassical approach known as the strong-field approximation (SFA). Both approaches predict comparable results and show the new features, but by using the semiclassical arguments behind the SFA and time-frequency analysis tools, we are able to fully understand the reasons for the cutoff extension.

Non-linear failure analysis of HCPB Test Blanket Module

For the European Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM) the reduced activation ferritic martensitic (RAFM) steel EUROFER 97 is selected as a structural material. During operation the TBM will be subjected to complex thermo-mechanical loadings which yield at certain positions of the structure to stresses beyond the design limits of the structural material. Preliminary structural analyses of the TBM have shown critical behavior in several key points of the structure. An improved design has been proposed and in order to identify and assess the problematic positions in the improved version of the TBM a non-linear failure analysis is performed, for which a coupled deformation damage model developed at KIT for RAFM steels and recently implemented in the finite element code ABAQUS is used. The thermal loads in the form of non-homogeneous temperature fields distributions are obtained from a thermal analysis performed using the finite element code ANSYS on the same structure. Importing the temperature fields into the finite element code ABAQUS and applying the remaining loads – coolant internal pressure and structural boundary conditions – non-linear simulations are conducted taking into account the ITER-typical cyclic nature of the loading. The simulation results are evaluated and discussed considering ratcheting and damage at most critical highly loaded areas of the structure.

The Influence of the Self–Rotation of the Planet on Its Motion Not Covered By Gravity Law

The self-rotation of the Earth solid inner core is analyzed to show the influence on the motion of the planet. Existing direction of the rotation gives new attracting force directed toward the Sun (~1011 N for the inner core only at this moment). The opposite direction of the self-rotation gives new rejecting force relative to our star. Corresponding similarity could be found in aerodynamics in the case of rotating or not rotating cylinder in the stream. The physical reasons for these results is based on the non-homogeneous gravity field of the Sun. Theoretically, the Earth could move toward the Sun during the millenniums (global warming) and contrary, out of the Sun, in the case of opposite self–rotation (ice period). Non-homogeneous gravity field of the Sun slows down angular velocity of the Earth in the case of existing self-rotation and accelerates the same one in another mentioned case.

Imaging of highly inhomogeneous strain field in nanocrystals using x-ray Bragg ptychography: A numerical study

X-ray ptychography is a lensless microscopy method able to provide extended field of view with spatial resolution above the diffraction limit. A series of intensity coherent diffraction patterns measured in the far field is used to obtain the numerical deconvolution between the sample scattering contrast and the illumination function. The measurements are performed with a finite-size beam spot scanned across the sample. The scan step, smaller than the beam size, ensures a high redundancy in the data set, which allows for the convergence of the iterative inversion algorithm. This work explores the possibility to use ptychography for the investigation of strained crystals by means of coherent x-ray Bragg diffraction, taking advantage of the high sensitivity to the atomic displacement fields. The Bragg diffraction scattering contrast is described by an effective complex-valued electron density, where the phase holds the information on the displacement field. The detailed two-dimensional numerical study of Bragg ptychography is presented, both for the known and unknown illumination cases. It demonstrates the high robustness of the ptychographical iterative engine for highly nonhomogeneous strain fields. In particular, the local information is extracted from the individual diffraction patterns to calculate the modulus and phase estimates of the electron density, which are further used to constrain the newly derived algorithm. From this work, it is foreseen that Bragg ptychography when experimentally feasible, will open the way to the nondestructive imaging of strain fields at the nanoscale.

On the polynomial vector fields on

Let X be a polynomial vector field of degree n on M, M = ℝm. The dynamics and the algebraic-geometric properties of the vector fields X have been studied intensively, mainly for the case when M = ℝm, and especially when n = 2. Several papers have been dedicated to the study of the homogeneous polynomial vector field of degree n on $\mathbb{S}^2$, mainly for the case where n = 2 and M = $\mathbb{S}^2$. But there are very few results on the non-homogeneous polynomial vector fields of degree n on $\mathbb{S}^2$. This paper attempts to rectify this slightly.

Electrostatic field effects on membrane domain segregation and on lateral diffusion.

Natural membranes are organized structures of neutral and charged molecules bearing dipole moments which generate local non-homogeneous electric fields. When subjected to such fields, the molecules experience net forces that can modify the lipid and protein organization, thus modulating cell activities and influencing (or even dominating) the biological functions. The energetics of electrostatic interactions in membranes is a long-range effect which can vary over distance within r-1 to r-3. In the case of a dipole interacting with a plane of dipoles, e.g. a protein interacting with a lipid domain, the interaction is stronger than two punctual dipoles and depends on the size of the domain. In this article, we review several contributions on how electrostatic interactions in the membrane plane can modulate the phase behavior, surface topography and mechanical properties in monolayers and bilayers.

Murine Cardiac Catheterizations and Hemodynamics: On the issue of Parallel Conductance

Catheter-based measurements are extensively used nowadays in animal models to quantify global left ventricular (LV) cardiac function and hemodynamics. Conductance catheter measurements yield estimates of LV volumes. Such estimates, however, are confounded by the catheter's nonhomogeneous emission field and the contribution to the total conductance of surrounding tissue or blood conductance values (other than LV blood), a term often known as parallel conductance. In practice, in most studies, volume estimates are based on the assumptions that the catheter's electric field is homogeneous and that parallel conductance is constant, despite prior results showing that these assumptions are incorrect. This study challenges the assumption for spatial homogeneity of electric field excitation of miniature catheters and investigated the electric field distribution of miniature catheters in the murine heart, based on cardiac model-driven (geometric, lump component) simulations and noninvasive imaging, at both systolic and diastolic cardiac phases. Results confirm the nonuniform catheter emission field, confined spatially within the LV cavity and myocardium, falling to 10% of its peak value at the ring electrode surface, within 1.1-2.0 mm, given a relative tissue permittivity of 33,615. Additionally, <1% of power leaks were observed into surrounding cavities or organs at end-diastole. Temporally varying parallel conductance effects are also confirmed, becoming more prominent at end-systole.