Optical trapping of nanoparticles on a silicon subwavelength grating and their detection by an ellipsometric technique

A method and setup are proposed for trapping and detecting nanoparticles dispersed in a nanocomposite solution using periodically localized light generated by a subwavelength transmission grating. By numerical simulations, it is shown that there is an optimum duty ratio of the grating to produce the periodically localized light. Experimental results are presented for Au/γ-Fe₂O₃ composite nanoparticles having a diameter of 21.0 nm trapped on a silicon subwavelength rectangular grating and detected ellipsometrically. The technique should prove useful for evaluating optical and mechanical properties of nanocomposite materials.     

The Model of a Surface Flaw and the Calculation of the Topography of Its Magnetic Field for Normal Magnetization by an Alternating Field. A Quasi-Stationary Case

A surface flaw model is proposed. The model describes the magnetic field topography H _d for normal magnetization by an alternating field H of frequency . It is shown that H _d can be presented as two cofactors: one cofactor describes a dependence of the topography on coordinates x, z and parameters of a flaw (depth h, opening width 2b), and another cofactor describes its dependence on the electrophysical properties of a tested material containing the surface flaw (specific conductivity , and the relative magnetic susceptibility ). Transition from the magnetostatic field of a flaw = 0 to a quasi-stationary field for magnetization under an alternating field H _0s of frequency is carried out using the model proposed for the magnetic field of a surface flaw under normal magnetization.     

Theoretical Fundamentals of Three-Parameter Testing of a Hardened Layer by an Asymmetric Electropotential Quasi-DC Probe: I. HL Model

A model of a hardened product in the form of half-space with piecewise linear variation of the specific resistance as a function of the depth in the surface layer is considered. The problem of the electrical potential distribution on the surface of the half-space is solved for a point supply of a low-frequency current to the half-space. An effective algorithm of solving the inverse problem of determining the layer parameters on the basis of the voltages measured on the surface is proposed. The possibility of testing cemented and nitrated layers of steel products by a probe with equidistant potential electrodes is investigated.     

Model of a Surface Flaw and Calculation of Topography of Its Magnetic Field for Tangential Magnetization by Alternating Magnetic Fields. Quasi-Stationary Case

A model of a surface flaw is proposed. The model describes topography of the magnetic field for tangential magnetization by an alternating magnetic field H at a frequency . It is shown that H can be represented in the form of two multipliers: one describes the dependence on the (X, Z) coordinates and the flaw parameters (the depth h and the opening width 2b) and the other describes the dependence on the electrophysical properties of the tested material in which the surface flaw is located (the specific conductivity and the relative magnetic permeability ). The computational model proposed makes it possible to describe the magnetic field topography ( = 0) reducing it to the quasi-stationary case and extend representations on the formation of magnetic fields induced by surface flaws with allowance of the magnetization frequency . The data on processing the experimental dependences in accordance with the proposed computational formulas give satisfactory results which confirm the validity of the computational model proposed in the study.     

The Microcomputer as an Intelligent Interface Between Laboratory Instruments and Data Systems: Automatic Data Collection from a Grain Analyzer

ABSTRACT

Data from a grain analyzer have been automatically read into a minicomputer data system using a single board microcomputer (KIM-I) as an intelligent serial line interface. The practicality of this type of data acquisition interface is discussed.     

Optical sectioning with a fluorescence confocal SLM: procedures for determination of the 2-D digital modulation transfer function and for 3-D reconstruction by tessellation

We have determined the operational parameters of a confocal scanning laser microscope (CSLM) used for fluorescence imaging. The system performance was characterized by the modulation transfer function (MTF), calculated from an edge response function (ERF) corresponding to a standard test pattern overlaying fluorescence solutions on a microscopic slide. Signal truncation error was avoided by making the ERF continuous at its limits through superposition of a suitable linear curve. We determined an appropriate scanning step density by defining a compromise between the requirements of the sampling theorem with respect to aliasing and the need for minimal suppression of higher spatial frequencies. These procedures for choosing the sampling density of the total digital CSLM permit a systematic optimization of the image acquisition parameters. A reproducible digital image was obtained, an important prerequisite for subsequent 3-D image reconstruction. The latter was accomplished by first developing and applying a maximally automated algorithm for finding closed and distinct contours (corresponding to objects in the 2-D optical sections). The missing information between contour loops was then interpolated by tessellation (triangulation) using a minimal polygon edge length criterion capable of describing closed surfaces even for adjacent contours with highly dissimilar geometries. In this procedure, we define an average shift length which compensates for the inherent disadvantage of run length encoding algorithms applied to different starting points in successive planes. The surface segments were used to calculate 3-D representations by applying a shading model, in the present applications specifically to chromosome I and the nucleolus of polytenized Chironomus thummi salivary gland nuclei.     

Flow ripple reduction of an axial piston pump by a combination of cross-angle and pressure relief grooves: Analysis and optimization

This paper investigates the potential of flow ripple reduction of an axial piston pump by a combination of cross-angle and pressure relief grooves. A dynamic model is developed to analyze the pumping dynamics of the pump and validated by experimental results. The effects of cross-angle on the flow ripples in the outlet and inlet ports, and the piston chamber pressure are investigated. The effects of pressure relief grooves on the optimal solutions obtained by a multi-objective optimization method are identified. A sensitivity analysis is performed to investigate the sensitivity of cross-angle to different working conditions. The results reveal that the flow ripples from the optimal solutions are smaller using the cross-angle and pressure relief grooves than those using the cross-angle and ordinary precompression and decompression angles and the cross-angle can be smaller. In addition, when the optimal design is used, the outlet flow ripples sensitivity can be reduced significantly.     

Piezoelectric and optical setup to measure an electrical field: application to the longitudinal near-field generated by a tapered coax

We propose a new setup to measure an electrical field in one direction. This setup is made of a piezoelectric sintered lead zinconate titanate film and an optical interferometric probe. We used this setup to investigate how the shape of the extremity of a coaxial cable influences the longitudinal electrical near-field generated by it. For this application, we designed our setup to have a spatial resolution of 100 microm in the direction of the electrical field. Simulations and experiments are presented.     

“Pull-in” of a pre-stressed thin film by an electrostatic potential: A 1-D rectangular bridge and a 2-D circular diaphragm

A one-dimensional (1-D) rectangular pre-stressed thin film clamped at two opposite ends is actuated by an electrostatic voltage applied to a pad directly underneath. The pre-stress is allowed to be either tensile or compressive in nature. At a critical applied voltage, the film becomes unstable and makes direct contact with the pad, leading to “pull-in”. An elastic model is constructed to account for the phenomenon over ranges of film-pad gap and residual stress. The results compare favorably with finite element analysis (FEA) in literature and experimental data, and possess distinct advantages over other available closed-form solutions. The model is further extended to a two-dimensional (2-D) axisymmetric diaphragm clamped at the periphery. Interrelationship between bridge-pad gap, residual membrane stress, critical voltage, and pull-in central deflection is derived such that new design criteria can be derived for micro-/nano-electromechanical devices. Implications for nano-structures are also discussed.     

Theoretical Fundamentals of Three-Parameter Testing of a Hardened Layer by an Asymmetric Electropotential Quasi-DC Probe: II. H and L Models

Simplified models of a hardened product in the form of a half-space with a homogeneous layer or a layer with linear variation of the specific resistance as a function of the depth are considered. The possibility of determining the layer parameters by means of voltages measured on the surface by a probe with equidistant potential electrodes is investigated. The probe is optimized with respect to the minimum of errors in the determined parameters with reference to homogeneous cemented and nitrated layers. Taking into account the random nature of the measurement errors, a well-posed (correct) measure of the local conditionality is introduced for a system of nonlinear equations determining the parameters of the object. The measure is proposed to be used for solving the problems of optimization of the transducer (probe).