Local spectral information in the near field with wavelet analysis and entropy

In near-field optical microscopy the resolution is strongly related to the experimental illumination conditions and to the separation between tip and sample. Therefore the spectral information in near-field data (related to the resolution in images) can be described only locally as a function of the tip-sample position. To make a local study of the spectral information in near-field data, we use wavelet decomposition that is associated with the calculation of entropy. We deduce the resolution from the characteristics of the wavelet, which leads to an automatic and numerical evaluation of the resolution in near-field data.     

Accurate field computation with the boundary element method

Interface problems in magnetostatics are formulated as boundary integral equations of the second kind involving the appropriate scalar (no current sources) or vector potentials. The boundary element method (BEM), which employs parametric representation of surfaces and sources, is used to solve some two-dimensional examples by way of illustration. A novel approach, automated to address Green's functions singularities over arbitrarily-shaped geometries, is introduced.     

Applications of excipients in the field of 3D printed pharmaceuticals

The aim of this study was to determine the effect of varying excipient content on the formation and physical properties of 3?D printed tablets. Fifteen different excipient preparations were formed into tablets with radii of 5?mm and thickness of 2?mm, using binder jetting (BJ). The tablets were analyzed by assessing visual and microstructural appearance, friability, hardness, and disintegration time. We found that filling agents with high water solubility (e.g. D-sucrose), binding agents with a high viscosity in solution (e.g. polyethylene glycol 4000) and moistening agent with higher water content can increase the bonding strength and hardness of the 3?D printed tablets and prolonged their disintegration time. This work has demonstrated that the type of excipient and its concentration affects the properties of the 3?D printed tablet. This article may be used as a guide for elucidation of the effects of using conventional tablet excipients in the field of 3?D printed pharmaceuticals. The present work should enable the identification of excipients that satisfy requirements, reduce analysis time, and improve efficiency.     

A finite deformation analysis of the near field surrounding the tip of crack-like elliptical perforations

A finite deformation analysis of the region surrounding the tip of crack-like elliptical perforations in an infinite plate under all around tension is presented as a model of the near field behavior of stress freezing photoelastic materials above critical temperature. The study is carried out in the deformed geometry and includes the effects of finite strains and rotations. A stress function is first introduced into the complete compatibility equations through linear constitutive relations; the resulting governing equation is solved through finite differences. The range of root radii investigated varies from one to nine times that of a deformed crack. Normal stresses and stress intensity factors are presented. The results of the analysis are compared to the linear analysis of Inglis. The effects of finite strains and rotations are shown to be large but are concentrated within a few root radii of the tip. Results suggest that the stress distribution near the notch root depends on the size of the root radius: small root radii produce maximum stresses away from the tip, whereas larger root radii produce maximum stresses at the tip itself. These effects are judged too local to influence photoelastic stress intensity determination.     

Electromechanical analysis of piezoelectric bimorph actuator in static state considering the nonlinearity at high electric field

This article contains electromechanical analysis of a piezoelectric bimorph actuator at high electric field by incorporating second-order constitutive equations of piezoelectric material. Tip deflection, block force, block moment, block load, output strain energy, output energy density, input electrical energy, and energy efficiency are analytically derived for the actuator at high electric field. The analysis shows that output energy and energy density increase more rapidly at high electric field, compared to the prediction by the linear model. The analysis shows energy efficiency depends on electric field. Some analytical results are validated with the published experimental results.     

Terahertz pulse propagation in the near field and the far field

We present a detailed investigation of the propagation properties of beams of ultrashort terahertz (THz) pulses emitted from large-aperture (LA) antennas. The large area of the emitter is demonstrated to have substantial influence on the temporal pulse profile in both the near field and the far field. We perform a numerical analysis based on scalar and vectorial broadband diffraction theory and are able to distinguish between near-field and far-field contributions to the total THz signal. We find that the THz beam from a LA antenna propagates like a Gaussian beam and that the temporal profile of the THz pulse, measured in the near field, contains information about the temporal and spatial field distribution on the emitter surface, which is intrinsically connected to the carrier dynamics of the antenna substrate. As a result of pulse reshaping, focusing of the THz beam leads to a reduced relative pulse momentum, with implications in THz field-ionization experiments.     

Optimizing the near field around silver tips

Owing to their promise of obtaining optical as well as topographic information in nanometer scale, apertureless near-field scanning optical microscopy (NSOM) and apertureless near-field scanning optical spectroscopy have drawn much attention recently. However, NSOM is still not a mature technique. A proper understanding of and the ability to tune the near field around the tip end is critically important in NSOM instrumentation and in NSOM image interpretation. On the basis of reflection geometry, we systematically studied the effects of a number of parameters pertinent in the application of apertureless NSOM, e.g., polarization, incident angle, wavelength of the incident laser, tip material, and tip length, by using the generalized field propagator technique. Our results show that all the above parameters have a significant influence on near-field enhancement and that care must be taken in the design of the experiment in order to maximize the near field. In addition to apertureless NSOM and spectroscopy, apertureless near-field lithography can benefit from these simulation results.     

Transition elements matching the near crack-tip strain field

New transition elements used with the collapsed triangular singular elements are constructed by using the improved isoparametric transformations. Without 1/r singular terms, the new transition elements' strain fields contain only % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaGymaiaac+% cadaGcaaqcaawaaiaadkhaaKqaGfqaaaaa!3B47!\[1/\sqrt r \] singularities and match the Williams solution quite well near the crack tip. It is convenient for the new transition elements to be constructed and introduced in the general purpose finite element programs by adding some modifications. Numerical results show that the transition elements possess good properties and are worth being applied to linear fracture computations.     

Information content of the near field: two-dimensional samples

Limits on the effective resolution of many optical near-field experiments are investigated. The results are applicable to variants of total-internal-reflection microscopy (TIRM), photon-scanning-tunneling microscopy (PSTM), and near-field-scanning-optical microscopy (NSOM) in which the sample is weakly scattering and the direction of illumination may be controlled. Analytical expressions for the variance of the estimate of the complex susceptibility of an unknown two-dimensional object as a function of spatial frequency are obtained for Gaussian and Poisson noise models, and a model-independent measure is examined. The results are used to explore the transition from near-zone to far-zone detection. It is demonstrated that the information content of the measurements made at a distance of even one wavelength away from the sample is already not much different from the information content of the far field.     

Information content of the near field: three-dimensional samples

We present an analysis of the accuracy and information content of three-dimensional reconstructions of the dielectric susceptibility of a sample from noisy, near-field holographic measurements, such as those made in scanning probe microscopy. Holographic measurements are related to the dielectric susceptibility via a linear operator within the accuracy of the first Born approximation. The maximum-likelihood reconstruction of the dielectric susceptibility is expressed as a linear combination of basis functions determined by singular value decomposition of the weighted measurement operator. Maximum a posteriori estimates based on prior information are also discussed. Semianalytical expressions are given for the likely error due to measurement noise in the basis function coefficients, resulting in effective resolution limits in all three dimensions. These results are illustrated by numerical examples.     

Magnetic field analysis by edge elements of magnetic components considering inhomogeneous current distribution within conductor windings

For magnetic field analysis by edge elements of the magnetic components, the method considering inhomogeneous current distribution within the conductor windings is investigated. To consider the inhomogeneous current distribution within the windings, we utilized the magnetic vector potential represented by edge elements and the current conservation equation represented by nodal elements in the region of the windings. In the first application, the eddy-current model, which has the conventional wire winding, was analyzed. For correct analysis using our method, it is required that all turns of the wire winding be divided into meshes. However, if the region of the wire winding does not exceed the winding window of the magnetic core, even the combination of our method and the solidly modeled wire winding enables us to correctly analyze the transformer and the inductor with conventional wire winding. In the second application, a flat transformer with conductor winding, such as a copper foil or sheet, was analyzed. The magnetic flux densities within the flat core and the inductance calculated by our method were in good agreement with the experiments. Thus, we confirmed the effectiveness of our method considering inhomogeneous current distribution within the conductor windings.     

Calculation of the near field of aggregates of arbitrary spheres

We study a numerical method of calculating the near field of ensembles of arbitrary spheres by extending Mie theory. A recursive method based on the orders of scattering is presented. This method represents a concise way to calculate the near field of aggregates of any number of arbitrary spheres, Numerical examples are given to show its validity.     

船舶近场声辐射特性初探

为了修正目前国内所普遍采用的船舶辐射噪声测量方法,建立了一个具有一定空间分布的船舶辐射噪声源模型。利用渡数积分方法仿真计算了该模型在自由场条件下的近程声场,并分析了近场辐射噪声的基本规律。仿真结果与国外文献提供的船舶水下辐射噪声近场特性吻合,验证了所建模型的正确性。     

Stress field near interface edge of elastic-creep bi-material

Stress fields on elastic-creep bi-material interfaces with different geometry of the interface edge are analyzed by finite element method. The results reveal that the stress highly concentrates near the interface edge at the loading instant and it gradually decreases as the creep-dominated zone expands from the small-scale creep to the large-scale creep. The stress singularity due to creep which resembles the HRR stress singularity appears near the interface edge in all cases. The stress intensity near the interface edge time-dependently decreases and becomes constant when the transition reaches the steady state. The magnitude is scarcely influenced by the edge shape of elastic material, though it depends on the edge shape of creep material. The stress intensity during the transition can be approximately predicted by the J-integral at the loading instant.     

提高丝网印刷ZnO纳米针场发射均匀性稳定性

针对现有的ZnO纳米针场发射均匀性、稳定性不良的问题,本文提出丝网印刷碳纳米管(CNTs)掺杂过滤的ZnO纳米针的方法来提高其均匀性和稳定性.场发射特性测试表明,ZnO纳米针经过滤后可以提高场发射均匀性,CNTs的掺杂提高了印刷ZnO纳米针薄膜的场发射电流密度和稳定性,印刷CNTs掺杂的ZnO纳米针薄膜在烧结温度为450℃时,印刷ZnO纳米针薄膜的场发射电流密度较高.该方法在ZnO纳米针场发射显示器的制作中有很好的实际应用价值.     

Temperature field near the singular line of the interface of anisotropic media

A representation of the temperature fields and the components of the vector of heat-flux density in both the base material (matrix) and the conjugate medium (inclusion) has been found for anisotropic media in the case of the interface with a singular line on condition of ideal thermal contact. It has been shown that the anisotropy of thermal properties makes it possible to do away with the singularity of the components of the heatflux-density vector. Particular cases of isotropy of the media and of heat-insulated and isothermal inclusions have been investigated. The results obtained are applicable for studying the nonstationary heat conduction of an anisotropic body with an uneven anisotropic inclusion. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 1, pp. 157–162, January–February, 2009.     

Modeling the stress field in laminated composite plates near discontinuities

A structural model is developed using Reissner's variational principle to analyze stress gradient problems in laminated composite plates. A statically admissible stress field, which has explicit dependence on the thickness coordinate, is selected for each layer. Both interlaminar traction and displacement continuity are enforced between layers. This model is similar to an earlier one developed by Pagano, but has four dependent variables less per layer than Pagano's model. It is shown that the model can duplicate Pagano's results for the same number of subdivisions through the thickness. The uniform axial extension of a [0/90]_s laminate is used as the example problem for comparison to Pagano's theory and to illustrate the methodology.     

Optical dipole model for photodetection in the near field.

Near-field photodetection optical microscopy (NPOM) is a scanning probe technique that has been developed to perform nanometer-scale optical intensity mapping and spectroscopy. In NPOM a nanometer-scale photodiode detector absorbs power directly as it is scanned in the near field of an illuminated sample surface. A model of photodetection in the near and intermediate fields is presented. A brief review of far-field absorption is given for comparison. Far-field absorption measurements measure the imaginary part of the polarizability to first order. In contrast, photodetection in the near field measures the real part of the polarizability. Other aspects of near-field photodetection are also examined, including contrast mechanisms and lateral resolution. NPOM measurements performed on isolated 300-nm spheres show good agreement with the theory.