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Previous studies on Z-scan have paid little attention to Z-scan transmittance about elliptical Gaussian beams in thick Kerr media. The purpose of this study is twofold. First, it proposes a new analytical approach to the Z-scan on-axis transmittance for elliptical Gaussian beams through the variational method. The analytical approach yields an explicit analytical solution (not numerically analyzed solution) for the Z-scan on-axis transmittance in arbitrary thick media, and then the explicit solution is generalized to circularly or elliptically symmetric Gaussian beams. With the analytical solutions, we explain the mechanism of the elliptical beam waist changes in both positive and negative Kerr media. Second, the proposed solutions are experimentally tested in the photorefractive LiNbO 3 :Fe crystal with a cw Ti:sapphire elliptical laser beam ( λ = 800 nm ), showing congruence between experimental data and the predicted values from the solutions. [ABSTRACT FROM AUTHOR]

Most of the existing electronic warfare systems use a threat library to identify radar signals. In this paper, new feature parameters for classifying various types of radar signals are introduced. The conventional method uses frequency, pulse repetition interval and pulse width sampled from the pulse description word column as characteristics of a signal. Such sampling technique cannot effectively model each radar signal when dealing with a complex signal array. This paper proposes probability moment and ApEn as an effective feature for the development of high-performance radar signal classifier. As shown in results, the proposed method can effectively classify ambiguous radar signals in the existing system because the signal values are similar but the order is different. In order to verify the performance of the proposed system, 100 types of radar signals in various bands were simulated, and the performance yielded 99% positive classification rate of the 100 radar signals. [ABSTRACT FROM AUTHOR]

Abstract: The two beam coupling (TBC) gains in porphyrin:Zn-doped nematic liquid crystals (NLCs) are greatly enhanced by adopting the grating translation technique with applying dc electric field. The maximum gain coefficient of , whose value is at least three times larger than that of no grating translation was obtained under the applied dc field of and the grating translation speed of . Based on the material and torque balance equations for NLCs taking into account the grating translation, we present the theoretical expressions for TBC gain enhancements, showing excellent agreement with the experimental results. [Copyright &y& Elsevier]

Abstract: We fabricated azo dye (methylorange) doped poly vinyl alcohol (MO/PVA) thin films and measured the photoinduced birefringence (PIB) kinetics for several pump beam intensities and for various MO concentrations by using the pump-probe technique. A novel approach to explain the transient behaviors of the photoinduced anisotropy is presented by employing an empirical stretched exponential time response in the course of the trans–cis–trans photoisomerization of azo molecules and is compared with the experimental data, showing excellent agreement. The stretched exponent is estimated to be β =0.34±0.04, revealing amorphous nature of the MO/PVA system. [Copyright &y& Elsevier]

Abstract: A new method has been investigated to improve the surface integrity of electro-chemical discharge machining (ECDM) process by use of conductive particles in the electrolyte. In conventional ECDM processes the generation of fine sparks with uniform energy has been most desired technique to improve the machining efficiency and the surface quality. However, precise control of the spark generations in ECDM process has been a challenging problem. In electrical discharge machining (EDM) processes, which is thermal erosion machining process using spark energy similar to the ECDM, powder-mixed EDM (PM-EDM) fluids have been used to improve machining quality. Although the exact role of the conductive particles in the EDM process could not be clearly explained yet, it has been reported that the powder stabilizes discharge current as a result of discharge energy dispersion. Considering the similarity of the ECDM process compared to EDM where electrical sparks are utilized, powder-mixed electrolyte was introduced to create similar effects. In this paper fine graphite powder (which has good thermal and electrical conductivity) mixed with electrolyte has been applied to the ECDM process. Borosilicate glass, which is frequently used as a material for micro structures, was used as a workpiece. To investigate effectiveness of the proposed method experiments were conducted. The experiment results demonstrated that the breakdown voltage was reduced and the peak current during the process was decreased by ten percents. Discharging pattern was modified such that a single discharge pulse was branched into two or three. As a result, the surface quality was improved compared to that from the conventional process. Various experiment results of product quality with respect to powders volume ratio are also presented. [Copyright &y& Elsevier]

Abstract: This paper uses a parameterized error model to analyze machine tool errors within the workspace and the methodology of on-machine measurement for improving the machining accuracy. Based on the rigid body kinematics, positioning errors derived using the homogeneous transformation matrices are parameterized by approximating error components with polynomial functions. Only fourteen measurement points are required to determine the model parameters and obtained from four diagonal measurements. A semi-sphere part was machined for the model verification with and without error compensation, and then measured with a touch trigger probe installed on the spindle while the part still stayed on the machine table. The results showed that the machining errors are reduced about 90, 78 and 92% in x, y, and z axes direction after error compensation. Also, the differences between OMM and CMM data were less than 5μm, concluding that the parts can be measured on the machine tool with a touch trigger probe with acceptable accuracy. [Copyright &y& Elsevier]

It is well known that the GC-rich discriminator region between the −10 region and the transcription start site is important for the stringent control of the transcription. However, the discriminator activity is influenced by flanking regions, in particular in conjunction with the promoter −35 and −10 sequences. In this study, we changed the sequence in the −35 region of the rnpB P-1 promoter to see how such changes affect the stringent control. The sequence variation in the −35 region changed the stringent signal. The change to the consensus TTGACA sequence caused the most prominent relieving effect on stringent repression of the rnpB transcription. The spacing between the −35 and −10 regions is also significant because the relieving effect of the TTGACA was offset by the change of the spacing from 17 to 16 bp. The nucleotide just upstream of the −35 region contributes toward generating stringent signals as well. [Copyright &y& Elsevier]

For examining the carrier movements through tunnel junction, electrically and optically-biased photoreflectance spectroscopy (EBPR and OBPR) were used to investigate the internal electric field in the InGaP/GaAs dual junction solar cell at room temperature. At InGaP and GaAs, the strength of p-n junction electric fields (Fpn) was perturbed by the external DC bias voltage and CW light intensity for EBPR and OBPR experiments, respectively. Moreover, the Fpn was evaluated using the Fast Fourier Transform (FFT) of the Franz—Keldysh oscillation from PR spectra. In the EBPR, the electric field decreased by increasing the DC bias voltage, which also decreased the potential barrier. In OBPR, when incident CW light is absorbed by the top cell, the decrement of the Fpn in the GaAs cell indicates that the photogenerated carriers are accumulated near the p-n junction. Photogenerated carriers in InGaP can pass through the tunnel junction, and the PR results show the contribution of the modification of the electric field by the photogenerated carriers in each cell. We suggest that PR spectroscopy with optical-bias and electrical-bias could be analyzed using the information of the photogenerated carrier passed through the tunnel junction. [ABSTRACT FROM AUTHOR]

Abstract This study was undertaken for improving the corrosion resistance, hardness, and toughness of SKD11, using the developed plasma diode electron beam equipment (PD-Ebeam). The SKD11 in this study is 1.5 w.t.% high-carbon steel; however, X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) analysis results after the PD-Ebeam treatment reveal that almost the entire iron matrix underwent an austenite phase transformation (F.C.C. crystal structure). Thus, an attempt is made to improve the hardness, toughness, and corrosion resistance using a characteristic of the austenite steel. A hardness enhancement of up to 680 (H.V.) could be achieved through PD-Ebeam heat and ultrasonic impact treatments. Further, the gamma structure sustainability and non-carbide formation were confirmed through the XRD and TEM analysis results. In addition, the friction coefficient in a wear test, was found to be lesser than that of vacuum heat-treated material, owing to the ductility of the gamma phase. As a result, it achieved 18% friction reduction, 47% reduction of wear, and corrosion resistance of level of the stainless steel (SUS304) compared to general vacuum heat treatment. [ABSTRACT FROM AUTHOR]

Mechanical machining of brittle material is difficult due to generation of fracture or cracks on machined surfaces. Glassy carbon (GC) is a brittle carbon material having outstanding mechanical and chemical characteristics making it suitable for use in glass molds. However, brittleness of GC makes its machining complicated and difficult. In order to fabricate GC surfaces with minimum cracks, hybrid machining processes utilizing electrochemical oxidation have been proposed. In the present study, a new, mixed acidic electrolyte incorporating a chemical oxidizer was utilized to improve the material removal rate of electrochemical oxidation assisted machining. Machining experiments were conducted to evaluate and to confirm the effect of the oxidizer-mixed electrolyte on material removal. [ABSTRACT FROM AUTHOR]

This study presents a new behavioral model for the magnetorheological (MR) fluid used in cylindrical rectilinear dampers. The model predicts variations in the magnetic energy density, shear stress, and viscoelastic behavior against an imposed strain along the axial direction under an axisymmetric magnetic field. Using the Lekner summation method, slow convergent magnetic interaction energy functions are transformed into rapidly convergent ones. The Maxwell constitutive model is coupled to the static model to take into account the viscoelastic behavior of the MR fluid. [ABSTRACT FROM AUTHOR]

Recently, many studies have been actively conducted to improve the mechanical properties of metallic materials through surface heat treatment with an electron beam. Thermionic focused electron beam equipment is mainly used in industrial manufacturing machines such as e-beam welders. However, such equipment is expensive, and the filament lifetime is limited. In this study, the austenite transformation in an iron matrix was investigated after surface heat treatment of SKD11 with plasma diode focused electron beam equipment, which is a recently developed alternative based on a plasma diode cold cathode. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results revealed that the iron matrix transformed to an austenite structure without Cr-rich carbide formation. After the surface heat treatment using the plasma diode focused electron beam equipment, a positive residual stress was confirmed by XRD residual stress measurements. This result was obtained because impurities in the iron matrix such as carbon existed in alloy form rather than composite form. The average hardness at a depth of 300 μm from the surface was measured to be approximately 480 Hv. [ABSTRACT FROM AUTHOR]

Abstract: A new method is presented for detecting the onset of ploughing during micromilling on the basis of the cutting force signal. The method utilises the variation in the peak values of the cutting force. Multiresolution analysis with the undecimated wavelet transform is used to detect the peak values of the cutting force signal. A ploughing-detection algorithm is developed, which compares the normalised variance in peak values with preset thresholds. The proposed method is verified by comparing the surface roughness of the sidewall under ploughing and normal cutting conditions in sidewall-machining experiments with a micromilling tool. [Copyright &y& Elsevier]

Abstract: Beam irradiation intervals are a critical parameter in the fabrication of nanopatterns via focused ion beam (FIB) milling. The beam irradiation intervals are defined in terms of the overlap. In this paper, the nanopattern height on a silicon surface is predicted using a mathematical FIB milling model that varies the overlap. The proposed model takes into account the angle dependence of the sputtering yield and redeposition effect, together with the superposition of a bi-Gaussian beam. The model was verified by comparing the results of a nanopattern machining experiment to those of a simulation based on the model. The simulation calculated the final two-dimensional geometry from ion milling parameters. The results of the simulation indicate that the proposed model is more precise than one that only considers the superposition of a Gaussian beam. [Copyright &y& Elsevier]

Abstract: In this paper a three-dimensional geometric simulation method of micro-EDM milling processes is proposed, which introduces a Z-map algorithm to precisely represent the geometries of a machined workpiece and the evolution of the tool shape caused by tool wear during the machining. The micro-EDM milling process is mathematically and geometrically modeled. In order to verify the performance of the developed simulator, an actual square cavity is machined and compared to the simulation result. The developed EDM simulator can be used for tool path generation for tool wear compensation as well as for prediction of tool wear. [Copyright &y& Elsevier]

Abstract: Demands for miniature components are rapidly increased in the field of optics, electronics, and medicine. Various machining methods have been introduced for the fabrication of complex three-dimensional microfeatures. However, burrs, which are an undesired but unavoidable by-product of most machining processes, cause many problems in assembly, inspection, process automation, and precision component operation. Moreover, as feature sizes decrease, burr problems become more difficult to resolve. To address this problem, several deburring methods for microfeatures have been introduced, including ultrasonic, magnetic abrasive, and electrochemical machining methods. However, these methods all have some shortcomings, such as mechanical damage, over-machining, changes in the material properties of the finished surface, sharp edge blunting, and the requirement for subsequent processing to remove chemical residues. In this study, microelectrical discharge machining (micro-EDM) using low discharge energy and a small-diameter cylindrical tool is introduced for deburring microfeatures. This method allows the machining of very small amounts of conductive materials regardless of the material hardness, and provides easy access to small microscale features for selective deburring. The burr geometry generated by the micromilling process was investigated to establish a deburring strategy using micro-EDM. The proposed method was verified by experimental results using aluminum, copper, and stainless steel workpieces. [Copyright &y& Elsevier]

Abstract: Magnetorheological (MR) fluid is used for various applications due to its controllable viscosity. To predict the behavior of MR fluid under certain three-dimensional (3D) magnetic and shear strain fields, it is essential to model the fluid in an appropriate manner. The behavioral models used in the previous research, however, have serious limitations because most of them oversimplify the inter-particle interactions and employ assumptions valid only under specific geometric configurations and field conditions. In this study, a new model that can predict the behavior of MR fluid under arbitrary 3D magnetic and shear strain fields is proposed. The present work considers an MR fluid configured as a 3D infinite lattice structure. Using the proposed model, the shear stress components themselves, not the dipolar interaction energy, are calculated directly to avoid the mathematical singularity otherwise encountered. The resulting stress functions of the proposed model are transformed into rapidly convergent functions using the Lekner summation method. Finally, the characteristics of the stiffened MR fluid under a magnetic field are investigated using the transformed functions. Numerical computations on the original and transformed functions are performed and compared under selected conditions to ensure the validity and prove the high convergence efficiency of the proposed model. [Copyright &y& Elsevier]

Abstract: The use of magnetorheological fluids for finishing is one of the most promising smart processes for the fabrication of ultra-fine surfaces, particularly three-dimensional millimeter or micrometer structures. This process is not readily applicable to hard-surface materials, like an Al2O3–TiC hard disk slider, if a conventional rotating tool is used. This is due to the rotational speed and the resulting actual impressed abrasion energy limits, and the consequent low efficiency of the material removal rate. In this study, the main mechanism responsible for the decrease of the material removal rate on hard materials for a wheel-type magnetorheological finishing process is examined, both theoretically and experimentally, and a solution to this problem is devised via two approaches. The first uses a rectilinear alternating motion to improve processing conditions, and the second focuses on the use of more effective abrasives, namely magnetizable abrasives made of iron powders sintered with carbon nanotubes, which are new abrasives that have not yet been introduced in the field of surface finishing. Furthermore, it is shown that these abrasives increase the lifetime of consumables (magnetorheological fluid and abrasives) and the material removal rate. [Copyright &y& Elsevier]

Abstract: A fabrication method of curved surfaces on silicon-based micro-structures using magnetorheological finishing is studied. Thorough explanations are made on the procedures for the evaluation and analysis of surface characteristics of a workpiece and on the fabrication method of the curved surface profile associated with the experiments using magnetorheological finishing. The effect of magnetic field around tool assembly on finished surface profiles is investigated using a finite element method (FEM). The analysis on the magnetic field is performed separately from that of the fluid flow field with the assumption that the field is weakly coupled to the working fluid at steady state with a certain geometric configuration adopted in this work. Several experiments were performed under controlled conditions and the results are demonstrated along with the physical interpretations thereof. The edge effect is turned out to be very important as the target workpiece gets smaller, which can be actively used for the fabrication of curved surfaces on millimeter-scale structures. Response surface methodology (RSM) is applied to predict the profile and roughness of the curved surface of the workpiece to be proceeded with a set of known experimental conditions. In order to use the RSM method, two control input and two response variables are chosen deliberately. Among the multi-regression models generally used in the modeling area, a second-order regression model is employed. The predicted results are verified through additional experiments performed independently. [Copyright &y& Elsevier]

A new finishing method for polishing local area of three-dimensional surface has been developed. The method utilizes the dielectrophoretic effect of abrasive particles, such as Al2O3, diamond, or SiC, in a suspension. The proposed method polishes the target surface with the collected layer of abrasive particles around a microtool caused by the dielectrophoretic effect. To model the behaviors of the abrasive particles dispersed in silicone oil under electric field, the dielectrophoretic characteristics of the abrasive particles are investigated. To verify the abrasive behavior model, the dielectrophoretic particle motions are captured in real-time with respect to various electric field conditions using a specially designed video recording system. The performance of proposed polishing method is evaluated using a borosilicate glass specimen. A dominant parameter to determine material removal rate is investigated and surface quality is evaluated using an atomic force microscope. [Copyright &y& Elsevier]