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  • Articles  (3,087)
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  • Applied Physics A  (1,984)
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  • Articles  (3,087)
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  • 1
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    Calibrated heat flow model for the determination of different heat-affected zones in single-pass laser-cut CFRP using a cw CO 2 laser (2014)
    Springer
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    Publication Date: 2014-12-18
    Description: Laser machining has great potential for automated manufacturing of parts made of carbon-fiber-reinforced plastic (CFRP) due to the nearly force and tool-wear free processing. The high vaporization temperatures and the large heat conductivity of the carbon fibers, however, lead to unintentional heat conduction into the material causing damage in zones close to the process. In this paper, the matrix damage zone (MDZ) is subdivided into a matrix sublimation zone (MSZ) where the matrix material was sublimated and a zone where the temperature temporarily exceeded a value causing structural damage in the matrix. In order to investigate the extent of these zones, a one-dimensional heat flow model was applied, which was calibrated by cutting experiments using temperature sensors embedded in the CFRP samples. The investigations showed that the extents of the MSZ and MDZ are dominated by a total interaction time, which includes the passage of the laser beam and the continued interaction of the cloud of hot ablation products with the carbon fibers at the kerf wall and that from a practical point of view, the experimentally determined effective heat conductivity is suitable for simple estimations of the heat-affected zones in CFRP.
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  • 2
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    Buckling of multi-walled silicon carbide nanotubes under axial compression via a molecular mechanics model (2014)
    Springer
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    Publication Date: 2014-12-18
    Description: This paper is concerned with the axial buckling behavior of multi-walled silicon carbide nanotubes (MWSiCNTs) based upon a molecular mechanics model. To this end, the mechanical properties of silicon carbide sheets are obtained according to the density functional theory within the framework of the generalized gradient approximation. Through establishing a linkage between the quantum mechanics and the molecular mechanics, the force constants of the total potential energy are obtained theoretically. A closed-form expression is proposed from which by knowing the chirality of the MWSiCNT, its critical buckling strain can be calculated as quickly and accurately as possible. The effects of chirality and number of walls on the critical buckling strain of MWSiCNTs are carefully investigated. It is concluded that with increasing the number of walls of nanotubes, their stability decreases. The effects of diameter and number of walls on the critical buckling strain of MWSiCNTs under axial load get more pronounced at lower diameters. Besides, it is found that the minimum critical buckling strain is related to nanotubes with \( (n,\frac{n}{2}) \) chiral vectors.
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  • 3
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    Fabrication of diamond microstub photoemitters with strong photoluminescence of SiV color centers: bottom-up approach (2014)
    Springer
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    Publication Date: 2014-11-11
    Description: Arrays of diamond photoemitters with silicon-vacancy (SiV) photoluminescent (PL) centers have been produced by epitaxy of CVD diamond inside laser-ablated channels in a-Si mask on single crystal or polycrystalline diamond substrates, the mask also serving as Si-doping source. Strong PL emission from the SiV centers with zero-phonon line at 738.6 nm wavelength (6 nm width, 0.8 ns decay time), localized within the photoemitters, has been measured.
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  • 4
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    Synthesis and microwave absorption properties of graphene/nickel composite materials (2014)
    Springer
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    Publication Date: 2014-11-11
    Description: Graphene/nickel composite materials were successfully prepared via a one-step in situ reduction from nickel chloride, graphene oxide, and hydrazine at 80 °C for 3 h. Face-centered cubic Ni nanostructures with uniform size and high dispersion assembled on graphene sheets. Through the measurement of complex relative permittivity and permeability, their microwave absorption properties were evaluated. In comparison with pure Ni nanoparticles and graphene, the composite materials demonstrated much better characteristics of microwave absorption. The lowest reflection loss value of the composites with a thickness of 3 mm can reach −23.3 dB at 7.5 GHz. Our research reveals that graphene/Ni composites are promising microwave absorption materials with desirable absorption properties and reduced material weight.
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  • 5
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    Determination of the carrier concentration in CdSe crystals from the effective infrared absorption coefficient measured by means of the photothermal infrared radiometry (2014)
    Springer
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    Publication Date: 2014-11-11
    Description: In this paper, a non-contact method that allows to determine the carrier concentration in CdSe crystals is presented. The method relies on the measurement of the effective infrared absorption coefficient by means of the photothermal infrared radiometry (PTR). In order to obtain the effective infrared absorption coefficient and thermal diffusivity, the frequency characteristics of the PTR signal were analyzed in the frame of a one-dimensional heat transport model for infrared semitransparent crystals. The carrier concentrations were estimated using a theory introduced by Ruda and a recently proposed normalization procedure for the PTR signal. The deduced carrier concentrations of the investigated CdSe crystals are in reasonable agreement with those obtained using Hall measurements and infrared spectroscopy. The method presented in this paper can also be applied to other semiconductors with the carrier concentration in the range of 10 14 –10 17  cm −3 .
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  • 6
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    Adhesion analysis of non-woven natural fibres in unsaturated polyester resin (2014)
    Springer
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    Publication Date: 2014-11-11
    Description: The presence of wool fibres in non-woven Alfa fibres sheet was investigated as a mean of improving adhesion of Alfa fibre-reinforced unsaturated polyester composite. FT-IR and Raman spectroscopy results revealed that such improvement could occur by a decrease in the hydrophilic character of the Alfa fibres owing to the presence of wool fibres. Hence, physical and chemical interactions could happen between the reinforcement and the matrix as demonstrated by FT-IR and Raman spectroscopy results. Tensile testing performed on this composite confirmed that such adhesion could occur according to its excellent specific parameters despite of its low tensile strength attributed to a higher fibre to fibre contact of wool fibres.
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  • 7
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    A high-quality multilayer structure characterization method based on X-ray fluorescence and Monte Carlo simulation (2014)
    Springer
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    Publication Date: 2014-11-11
    Description: X-ray fluorescence (XRF) is a well known nondestructive technique. It is also applied to multilayer characterization, due to its possibility of estimating both composition and thickness of the layers. Several kinds of cultural heritage samples can be considered as a complex multilayer, such as paintings or decorated objects or some types of metallic samples. Furthermore, they often have rough surfaces and this makes a precise determination of the structure and composition harder. The standard quantitative XRF approach does not take into account this aspect. In this paper, we propose a novel approach based on a combined use of X-ray measurements performed with a polychromatic beam and Monte Carlo simulations. All the information contained in an X-ray spectrum is used. This approach allows obtaining a very good estimation of the sample contents both in terms of chemical elements and material thickness, and in this sense, represents an improvement of the possibility of XRF measurements. Some examples will be examined and discussed.
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  • 8
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    Persian turquoise glazed bodies: reproduction and optical properties (2014)
    Springer
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    Publication Date: 2014-11-11
    Description: Ancient turquoise Persian glazed ceramics, which are well known as Khar-Mohreh, belonged to several centuries ago. In this research, reproduction of ancient glazed bodies was performed, and the products were studied by different techniques. Experimental evaluations were focused on elemental, structural, morphological, and colorimetric characteristics. SEM micrographs illustrated a thin (10 μm) uniform composite glazed layer on a porous composite thicker layer (500 μm). The layers consist of microneedle-shaped and nanospherical particles of copper oxide distributed in an amorphous silicate medium. Modeling of this architecture was used for determination of the visual aspect of the ceramic via the reflectance coefficient. Structural and colorimetric results showed that the shape and distribution of copper oxide particles do not play a crucial role on the color of these ceramics.
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  • 9
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    Multi-particle FEM modeling on microscopic behavior of 2D particle compaction (2014)
    Springer
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    Publication Date: 2014-11-11
    Description: In this paper, the discrete random packing and various ordered packings such as tetragonal and hexagonal close packed structures generated by discrete element method and honeycomb, which is manually generated were input as the initial packing structures into the multi-particle finite element model (FEM) to study their densification during compaction, where each particle is discretized as a FEM mesh. The macro-property such as relative density and micro-properties such as local morphology, stress, coordination number and densification mechanism obtained from various initial packings are characterized and analyzed. The results show that the coupling of discrete feature in particle scale with the continuous FEM in macro-scale can effectively conquer the difficulties in traditional FEM modeling, which provides a reasonable way to reproduce the compaction process and identify the densification mechanism more accurately and realistically.
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  • 10
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    Negative and positive magnetoresistance in GaInNAs/GaAs modulation-doped quantum well structures (2014)
    Springer
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    Publication Date: 2014-11-11
    Description: In this work, magnetoresistance of as-grown and annealed n- and p-type modulation-doped Ga 0.68 In 0.32 N y As 1−y /GaAs single quantum well structures with various nitrogen concentrations has been studied. At low temperatures and low magnetic fields, in n-type samples negative and in p-type samples positive, magnetoresistance has been observed. The observed negative magnetoresistance in n-type samples is an indication of enhanced backscattering of electrons due to the weak localization of the electrons as an effect of the N-induced defects. Nitrogen concentration and thermal annealing dependence of the magnetoresistance have been studied for both n- and p-type samples. The observed decrease in the negative magnetoresistance in n-type and enhanced positive magnetoresistance in p-type samples following thermal annealing have been explained by considering thermal annealing-induced improvement of mobility and the crystal quality in N-containing samples. After thermal annealing, the magnitude of negative magnetoresistance decreases and the breaking of the weak localization is achieved at lower magnetic fields in n-type samples. It is observed that as the mobility of the sample increases, critical magnetic field of negative to positive magnetoresistance transition becomes lower.
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  • 11
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    The future of focused electron beam-induced processing (2014)
    Springer
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    Publication Date: 2014-11-11
    Description: A perspective is sketched for the field of focused electron beam-induced processing (FEBIP). The FEBIP lithography technique is compared to the very successful resist-based electron beam lithography (EBL) technique. The advantages of FEBIP over EBL are identified, the main advantage being its high spatial resolution. This will enable FEBIP to become an important lithography technique for the fabrication of devices with critical dimension in the range between 1 and 20 nm and serve as a complementary technique to EBL. It will be discussed what needs to be done to achieve this and what the potential applications are.
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  • 12
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    Dynamics of ultrashort pulsed laser radiation induced non-thermal ablation of graphite (2014)
    Springer
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    Publication Date: 2014-11-11
    Description: We report on the dependence of a laser radiation induced ablation process of graphite on the applied pulse duration of ultrashort pulsed laser radiation smaller than 4 ps. The emerging so-called non-thermal ablation process of graphite has been confirmed to be capable to physically separate ultrathin graphitic layers from the surface of pristine graphite bulk crystal. This allows the deposition of ablated graphitic flakes on a substrate in the vicinity of the target. The observed ablation threshold determined at different pulse durations shows a modulation, which we ascribe to lattice motions along the c axis that are theoretically predicted to induce the non-thermal ablation process. In a simple approach, the ablation threshold can be described as a function of the energy penetration depth and the absorption of the applied ultrashort pulsed laser radiation. Based on the analysis of the pulse duration dependence of those two determining factors and the assumption of an invariant ablation process, we are able to reproduce the pulse duration dependence of the ablation threshold. Furthermore, the observed pulse duration dependences confirm the assumption of a fast material specific response of graphite target subsequent to optical excitation within the first 2 ps.
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  • 13
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    Determination of Na acceptor level in Na + ion-implanted ZnO single crystal (2014)
    Springer
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    Publication Date: 2014-11-11
    Description: Ion implantation was used to dope Na acceptor into ZnO single crystals. With three mixed implantation energies, uniform depth distribution of Na ion in the surface region (~300 nm) of ZnO bulk crystals is achieved. Via post-implantation annealing, a donor–acceptor pair recombination band is identified in the low-temperature photoluminescence spectra, from which the energy level of Na-related acceptor in single crystalline ZnO is estimated to be 300 meV. A p–n junction based on this ZnO–Na layer shows rectifying characteristics, confirming the p-type conductivity.
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  • 14
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    Femtosecond laser color marking stainless steel surface with different wavelengths (2014)
    Springer
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    Publication Date: 2014-11-11
    Description: The femtosecond laser color marking stainless steel surfaces with different incident wavelengths were investigated theoretically and experimentally. It indicates that the spectral regions of the colors firstly increase and then reduce with increasing spatial periods of the ripples induced by laser irradiation. Additionally, the colors are gradually changed from blue to red due to the elongation of the diffracted light wavelengths. As a result, the color effects are distinctly different. This study offers a new controllable parameter to produce diverse colors, which may find a wide range of applications in the laser color marking, art designing and so on.
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  • 15
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    Tuning charge transport in pentacene thin-film transistors using the strain-induced electron–phonon coupling modification (2014)
    Springer
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    Publication Date: 2014-11-11
    Description: Tuning charge transport in the bottom-contact pentacene-based organic thin-film transistors (OTFTs) using a MoO x capping layer that serves to the electron–phonon coupling modification is reported. For OTFTs with a MoO x front gate, the enhanced field-effect carrier mobility is investigated. The time domain data confirm the electron-trapping model. To understand the origin of a mobility enhancement, an analysis of the temperature-dependent Hall-effect characteristics is presented. Similarly, the Hall-effect carrier mobility was dramatically increased by capping a MoO x layer on the pentacene front surface. However, the carrier concentration is not affected. The Hall-effect carrier mobility exhibits strong temperature dependence, indicating the dominance of tunneling (hopping) at low (high) temperatures. A mobility enhancement is considered to come from the electron–phonon coupling modification that results from the contribution of long-lifetime electron trapping.
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  • 16
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    Effect of Sb additive on structural and optical properties of Se–Te–Sb thin films (2014)
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    Publication Date: 2014-11-11
    Description: Amorphous Se 85− x Te 15 Sb x ( x  = 2.5, 5 and 7.5 at.%) thin films were deposited on glass substrates by thermal evaporation. The absorption coefficient was determined from the transmittance, and reflectance spectra in the wavelength range 400–2500 nm. Various optical constants have been calculated for the studied compositions. The mechanism of the optical absorption follows the rule of non-direct transition. It was found that the optical energy gap, E g , decreases from 1.42 to 1.36 eV with increasing Sb content from 2.5 to 7.5 at.%. These results can be interpreted on the basis of the chemical bond approach proposed by Bicermo and Ovshinsky. On the other hand, the optical constants such as refractive index, n , and extinction coefficient, K ex , of the films were studied. The dispersion of the refractive index was discussed in terms of single-oscillator Wemple–DiDomenico model. The influence of Sb content on the structure for the annealed films was investigated using X-ray diffraction (XRD) and scanning electron microscopy. The average particle size of the crystalline size for Te 0.04 Se 0.96 phase deduced from XRD pattern. This average decreases with increasing Sb content.
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  • 17
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    Ag y :TiN x thin films for dry biopotential electrodes: the effect of composition and structural changes on the electrical and mechanical behaviours (2014)
    Springer
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    Publication Date: 2014-12-19
    Description: In the present work, Ag y :TiN x thin films, obtained by reactive DC magnetron sputtering, with decreasing [N]/[Ti] atomic ratios (from 1 to 0.1) and a fixed amount of Ag pellets placed in the erosion zone of a pure Ti target, were studied envisaging their application as biopotential electrodes. The strongly under-stoichiometric samples, [N]/[Ti] = 0.1 and 10 at.% Ag; [N]/[Ti] = 0.2 and 8 at.% Ag, were found to be composed of a N-doped hcp-Ti structure, with possible formation of TiAg or Ti 2 Ag intermetallics. These samples exhibit high electrical resistivity values and low hardness and reduced modulus. In the set of samples indexed to a transition zone, [N]/[Ti] = 0.3 and 15 at.% Ag; [N]/[Ti] = 0.7 and 32 at.% Ag, a hcp-Ti to fcc-TiN phase transformation took place, giving rise to a disaggregated N-deficient TiN matrix. It correlates with the high resistivity values as well as the higher hardness and reduced modulus values that were obtained. The last identified zone comprised the stoichiometric Ag:TiN x sample—[N]/[Ti] = 1 and 20 at.% Ag. Extensive metallic Ag segregation was detected, contributing to a significant decrease of the resistivity and hardness values.
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  • 18
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    Removal of Verrucaria nigrescens from Carrara marble artefacts using Nd:YAG lasers: comparison among different pulse durations and wavelengths (2014)
    Springer
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    Publication Date: 2014-12-19
    Description: The periodical removal of biodeteriogens is a fundamental need for the preservation of outdoor stone cultural heritage, which is stimulating significant efforts toward the development of low-impact conservation strategies. In the present work, the potential of laser removal of Verrucaria nigrescens Pers. from Carrara marble and the evaluation of the associated biocide effect on the organism residues embedded in the surface texture and through the outer porosities of the stone substrate were investigated. The fundamental wavelength of Nd:YAG laser (1,064 nm), commonly used in stone cleaning, and its second harmonic (532 nm) were comparatively tested. The phenomenology of laser treatments carried out in different irradiation conditions was characterized using optical, epifluorescence, and electron microscopes along with chlorophyll fluorescence with pulsed amplitude-modulated imaging. The results achieved show that 532 nm can provide significant advantages with respect to 1,064 nm. The potential of the latter against the biodeteriogens appears rather limited because of the low optical absorption, whereas the former can allow effective and practicable laser treatments, which disclose a significant application perspective.
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  • 19
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    Metal/InGaN Schottky junction solar cells: an analytical approach (2014)
    Springer
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    Publication Date: 2014-12-09
    Description: The photovoltaic behaviour of metal/n-InGaN Schottky junction solar cells with low- and high-level injection conditions are explored by using voltage model. Four metals Ni–Au, Ni, Au and Pt are used as Schottky contact with n-InGaN and Schottky junction solar cell studied for open-circuit voltage ( V oc ) and short circuit current density ( J sc ) with a variation of Indium composition in n-InGaN. The cut-off value of Indium composition in n-InGaN is 36, 42, 55 and 70 % for Ni–Au, Ni, Au and Pt, respectively. The effects of doping density and surface recombination velocity on V oc and J sc are also explored. Model predict increment in V oc and J sc under high-level injection condition as compared to low-level injection condition with ϕ  = 2 × 10 17  cm −2  s −1 photon flux. The metal, Pt, is found to be a better choice in terms of making Schottky junction with n-InGaN. The concentration of donor atoms in n-InGaN plays an important role in both types of injection. The donor concentration should preferably be kept higher (〉10 16  cm −3 ) to get higher V oc .
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  • 20
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    Synthesis and the enhanced visible-light-driven photocatalytic activity of BiVO 4 nanocrystals coupled with Ag nanoparticles (2014)
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    Publication Date: 2014-12-09
    Description: BiVO 4 nanocrystals coupled with Ag nanoparticles (Ag–BiVO 4 heterogeneous nanostructures) have been prepared by a new strategy via combining a hydrothermal route with a polyol process, in which BiVO 4 nanocrystals were first synthesized by a hydrothermal route, and then, Ag nanoparticles were grown on the surfaces of the presynthesized BiVO 4 nanocrystals through a polyol process. The photocatalytic evaluations demonstrate that BiVO 4 nanocrystals coupled with Ag nanoparticles exhibit the enhanced visible-light-driven photocatalytic activity for the degradation of methylene blue (MB) and rhodamine B (RhB). The energy alignment and diffuse reflectance property of Ag–BiVO 4 heterogeneous nanostructures demonstrate that Ag nanoparticles attached on the surfaces of BiVO 4 nanocrystals play double roles for the enhanced visible-light-driven photocatalytic activity. First, the Ag nanoparticles grown on the surfaces of BiVO 4 nanocrystals may act as electron sinks to retard the recombination of the photogenerated electrons and holes in BiVO 4 so as to improve the charge separation on its surfaces. Second, the Ag nanoparticles increase the visible light absorption of the Ag–BiVO 4 photocatalyst due to surface plasmon resonance (SPR) of Ag nanoparticles. These double roles of Ag nanoparticles make Ag–BiVO 4 heterogeneous nanostructures to exhibit the enhanced photocatalytic activity to decompose MB and RhB under visible light irradiation, compared to the pure BiVO 4 nanocrystals. The enhanced photocatalytic activity is attributed to the charge transfer from BiVO 4 to the attached Ag nanoparticles as well as SPR absorption of Ag nanoparticles. The present work not only provides an efficient route to enhance visible-light-driven photocatalytic activity of BiVO 4 , but also offers a new strategy for fabricating metal–semiconductor heterogeneous nanostructure photocatalysts, which are expected to show considerable potential applications in solar-driven wastewater treatment and water splitting.
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  • 21
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    Enhanced hydrogen adsorption by Fe 3 O 4 –graphene oxide materials (2014)
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    Publication Date: 2014-12-18
    Description: In the present work, graphene oxide (GO) was prepared by hummers method from natural graphite and modified with iron oxide nanoparticles. The structural order and textural properties of the graphene-based materials were studied by TEM, XRD, TG-DTA and FT-IR. Hydrogen adsorption measurements have been carried out at 77 or 87 K, and atmospheric pressure on graphene oxide and Fe 3 O 4 –graphene oxide materials. Hydrogen adsorption at 77 K and atmospheric pressure reached values in the order of 1.7 and 2.1 wt% for graphene oxide and Fe 3 O 4 –graphene oxide materials, respectively. The hydrogen adsorption capacities of the Fe 3 O 4 –graphene oxide materials compare favorably well with those attained with high-value carbon materials. The isosteric heat of adsorption ( Q st ) was investigated as a function of hydrogen uptake at 77 and 87 K over the pressure range of 0 to atmospheric pressure. The isosteric heat of adsorption for magnetic GO (9.7 kJ mol −1 ) was found to be higher than for GO (6.1 kJ mol −1 ).
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  • 22
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    Leakage current reduction in junctionless tunnel FET using a lightly doped source (2014)
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    Publication Date: 2014-12-18
    Description: In this paper, we explain the problem of dramatic OFF-state leakage in junctionless tunnel field effect transistor (JLTFET) for a channel thickness greater than 10 nm. In JLTFET, with channel width greater than 10 nm, the depletion region primarily remains confined below the dielectric–semiconductor interface. Hence, we tend to incur significant leakage through the center of the device. With the help of 2D device simulations, we demonstrate that the cause of the leakage current is predominantly due to thermal injection in the source region and is concentrated through the center of the device. We suggest a technique of using a lightly doped source region, below the p-gate to increase the barrier and prevent any leakage. The proposed alteration records an improved I ON / I OFF ratio for JLTFET for a channel of width 20 nm.
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  • 23
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    Light extraction improvement of blue light-emitting diodes with a Metal-distributed Bragg reflector current blocking layer (2014)
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    Publication Date: 2014-12-07
    Description: The p-electrode of blue light-emitting diodes (LED) chips has a low transmittance on the blue light spectrum. The blue light emitted from the quantum wells under the p-electrode will be severely absorbed by p-electrode, which cause a decrease in blue light extraction efficiency (LEE). In this study, we first designed a current blocking layer (CBL) structure with the blue light reflection through the simulation software. The simulation results show that this structure can effectively improve blue LEE, and then, this structure was verified by experiment. Electroluminescence measurement results show that LED with Metal-distributed Bragg reflector (M-DBR) CBL exhibited better optical performance than the LED with SiO 2 CBL and DBR CBL. It was found that M-DBR CBL can effectively increase the blue light reflectivity and prevent the light absorption from the metal p-electrode to improve LED’ blue LEE.
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  • 24
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    The mysterious halos in iron gall ink manuscripts: an analytical explanation (2014)
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    Publication Date: 2014-12-07
    Description: Three historical manuscripts, two on parchment (dated 1280 and 1514) and one on paper support (dated 1589–1592), were under study. The three manuscripts were strongly attacked by microorganisms exhibiting dark brownish stains all over the surface except in the adjacent areas to some of the used inks, where a halo around the written text could be observed. In order to understand the origin of these halos, inks and manuscript supports were analyzed using portable energy-dispersive X-ray spectroscopy. Characteristic elements (Fe, Cu, Zn, and Mn) from iron gall inks were identified. Inks surrounded by a halo had in common a high amount of Zn in their composition. Microbiologic assays were performed aseptically on collected samples from the areas of the document with significant contamination and degradation. Samples were inoculated in a selective culture media, and the microorganisms developed were identified according to the macroscopic and microscopic features. For the evaluation of microflora proliferation, scanning electron microscopy was used. Furthermore, in vitro tests were carried out in the presence of zinc sulfate, revealing inhibition capacity for the majority of fungi sampled from these manuscripts.
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    Ultrasound-assisted synthesis of porous Co 3 O 4 microrods and their lithium-storage properties (2014)
    Springer
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    Publication Date: 2014-12-19
    Description: Porous Co 3 O 4 microrods have been prepared by an ultrasound-assisted route with subsequent calcination. The as-prepared Co 3 O 4 microrods are composed of interconnected nanoparticles with porous characteristics. The ultrasonic irradiation is critical to determine the morphology and the electrochemical performance of the products. When tested as anode material for lithium-ion battery, the porous Co 3 O 4 microrods show improved capacity and rate cycling performance. The reversible capacity of the materials retains 678 (±5) mAh g −1 after 50 cycles at 100 mA g −1 . Even when cycled at various rate for more than 50 cycles, the reversible capacity recovers to 600 (±5) mAh g −1 for the current of 100 mA g −1 . The improved lithium-storage performance can be attributed to the reduced electrochemical reaction resistance due to the unique porous architecture of Co 3 O 4 microrods.
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    High-mobility transparent thin-film transistors with ZnSnLiO channel layer prepared by radio frequency magnetron sputtering (2014)
    Springer
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    Publication Date: 2014-12-19
    Description: We have fabricated transparent thin-film transistors with ZnSnLiO as active layers deposited by radio frequency magnetron sputtering at room temperature. The TFTs structure used in this study was a staggered bottom-gate, which consists of SiO 2 as a gate insulator and heavily doped p-type Si(1 1 1) as a gate electrode. In order to optimize the performance of the ZnSnLiO thin-film transistors, the thermal annealing is investigated. We find that appropriate annealing temperature is very beneficial for the ZnSnLiO TFTs, and when the annealing temperature is 500 °C, the transistor exhibited the high field-effect mobility of 45.1 cm 2 /V s and a large I on/off ratio of 6.0 × 10 7 .
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    Femtosecond laser fabricating black silicon in alkaline solution (2014)
    Springer
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    Publication Date: 2014-12-04
    Description: An efficient approach for enhancing the surface antireflection is proposed, in which a black silicon is fabricated by a femtosecond laser in alkaline solution. In the experiment, 2 wt% NaOH solution is formulated at room temperature (22 ± 1 °C). Then, a polished silicon is scanned via femtosecond laser irradiation in 2 wt% NaOH solution. Jungle-like microstructures on the black silicon surface are characterized using an atomic force microscopy. The reflectance of the black silicon is measured at the wavelengths ranging from 400 to 750 nm. Compared to the polished silicon, the black silicon can significantly suppress the optical reflection throughout the visible region (〈5 %). Meanwhile, we also investigated the factors of the black silicon, including the femtosecond laser pulse energy and the scanning speed. This method is simple and effective to acquire the black silicon, which probably has a large advantage in fast and cost-effective black silicon fabrication.
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    Nitrogen-doped and gold-loaded TiO 2 photocatalysts synthesized by sequential reactive pulsed laser deposition (2014)
    Springer
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    Publication Date: 2014-01-12
    Description: Nitrogen-doped titanium oxide thin films covered by gold metal nanoparticles were grown on (001) SiO 2 quartz substrates by pulsed laser deposition. A KrF* excimer laser source ( λ  = 248 nm, τ FWHM  ≤ 25 ns, ν  = 10 Hz) was used for the irradiation of TiO 2 and gold metal targets. The experiments were performed in controlled reactive oxygen or nitrogen atmosphere. The layers were grown for photocatalytic applications. Evaluation of photocatalytic activity was performed by photodegradation of methyl orange under near-UV light irradiation. Our results show that nitrogen doping and addition of gold nanoparticles have complementary effects, photoactivity being significantly improved as compared to that of pure titanium oxide.
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    High-rate reactive magnetron sputtering of zirconia films for laser optics applications (2014)
    Springer
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    Publication Date: 2014-01-18
    Description: ZrO 2 exhibits low optical absorption in the near-UV range and is one of the highest laser-induced damage threshold (LIDT) materials; it is, therefore, very attractive for laser optics applications. This paper reports explorations of reactive sputtering technology for deposition of ZrO 2 films with low extinction coefficient k values in the UV spectrum region at low substrate temperature. A high deposition rate (64 % of the pure metal rate) process is obtained by employing active feedback reactive gas control which creates a stable and repeatable deposition processes in the transition region. Substrate heating at 200 °C was found to have no significant effect on the optical ZrO 2 film properties. The addition of nitrogen to a closed-loop controlled process was found to have mostly negative effects in terms of deposition rate and optical properties. Open-loop O 2 gas-regulated ZrO 2 film deposition is slow and requires elevated (200 °C) substrate temperature or post-deposition annealing to reduce absorption losses. Refractive indices of the films were distributed in the range n  = 2.05–2.20 at 1,000 nm and extinction coefficients were in the range k  = 0.6 × 10 −4 and 4.8 × 10 −3 at 350 nm. X-ray diffraction analysis showed crystalline ZrO 2 films consisted of monoclinic + tetragonal phases when produced in Ar/O 2 atmosphere and monoclinic + rhombohedral or a single rhombohedral phase when produced in Ar/O 2  + N 2 . Optical and physical properties of the ZrO 2 layers produced in this study are suitable for high-power laser applications in the near-UV range.
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    A Comparison of Standard One-Step DDA Circular Interpolators with a New Cheap Two-Step Algorithm (2014)
    Hindawi
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    Publication Date: 2014-01-21
    Description: We present and study existing digital differential analyzer (DDA) algorithms for circle generation, including an improved two-step DDA algorithm which can be implemented solely in terms of elementary shifts, addition, and subtraction.
    Print ISSN: 1687-5591
    Electronic ISSN: 1687-5605
    Topics: Computer Science , Technology
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    Impact of amorphization on the magnetic state and magnetocaloric properties of Gd 3 Ni (2014)
    Springer
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    Publication Date: 2014-01-22
    Description: Rapid quenching and ball milling have been used to modify the magnetic state and magnetocaloric properties of the intermetallic compound Gd 3 Ni. The melt-spun and ball-milled Gd 3 Ni samples are found to exhibit a soft ferromagnetic-like behavior below 120 K, whereas in the crystalline state, the Gd 3 Ni compound is an antiferromagnet with a Néel temperature of about 99 K. The reduced value of the saturation magnetization observed in amorphous Gd 3 Ni samples is ascribed to the appearance of a magnetic moment on Ni atoms. After amorphization, the Gd 3 Ni samples exhibit substantially improved magnetocaloric properties in a low field region in comparison with crystalline Gd 3 Ni.
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    Effective Phase Tracking for Bioinspired Undulations of Robotic Fish Models: A Learning Control Approach (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
    Details
    Publication Date: 2014-01-22
    Description: Robotic models have been used as one of the approaches to study fish locomotion. Therefore, this paper proposes an effective control scheme that enables robotic models to mimic fin-ray undulation kinematics of live fish. We found in the experiments of robotic fin undulation that the difference between the desired and actual trajectories can be significant. It is believed that the difference might be caused by the phase lagging effect. To tackle the phase tracking problem, a modified iterative learning control (ILC) scheme is proposed and implemented on the robotic fish model. Furthermore, a memory clearing operator is proposed to satisfy the Lipschitz condition. This is necessary for the convergence and feasibility of the ILC scheme. Finally, experimental results illustrate the effectiveness of the proposed learning control approach, including the memory clearing operator.
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    Runout Tracking in Electric Motors Using Self-Mixing Interferometry (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: In this paper, a self-mixing interferometry sensor has been used as a proximity probe to measure possible runout in permanent magnet synchronous motors, for fault diagnosis. A general procedure for the measurement of the 2-D trajectory of the motor shaft is described in detail, including procedures for the characterization of the uncertainty due to the shape of the shaft, and the management of speckle noise. The performance of the proposed sensor has been compared to that of a commercial Polytec laser vibrometer, for validation purposes. Results show inaccuracies in the order of ±6 μm, which agree well with the measured uncertainty introduced by shaft surface imperfections.
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    Integrated PID-Based Sliding Mode State Estimation and Control for Piezoelectric Actuators (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: Tracking control of piezoelectric actuators (PEAs) has stimulated the development of various advanced control schemes that utilize the feedback of PEA system states for improved control performance. Among them, the one based on the concept of sliding mode has been shown promising due to its robustness to matched uncertainties, but leaving the required state estimation to be desired. Previous studies show that the PEA can be modeled as a linear dynamic system with matched uncertainties. On this basis, this paper presents the development of a novel observer based on the concept of proportional-integral-derivative-based (PID-based) sliding mode, in which the switching function is replaced by a PID regulator. The novel observer, referred to as the PID-based sliding mode observer (PIDSMO), relaxes the observer matching condition as required in the use of the unknown-input observers. The PIDSMO is then integrated with the PID-based sliding mode controller (PIDSMC) to form a novel integrated PID-based sliding mode observer-controller (PIDSMOC) for PEA tracking control. Experiments performed on a PEA showed that the PIDSMO can accurately estimate the PEA states and that the integrated PIDSMOC can achieve better tracking control performances as compared to the PIDSMC with α–β filter control scheme.
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    Implementation and Performance Analysis of Digital Controllers for Brushless DC Motor Drives (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper presents design and digital implementation of a fuzzy controller for achieving improved performance of Brushless dc (BLDC) servomotor drive. The performance of fuzzy and PID controller-based BLDC servomotor drives is investigated under different operating conditions such as change in reference speed, parameter variations, load disturbance, etc. BLDC servomotors are used in aerospace, instrumentation systems, space vehicles, electric vehicles, robotics, and industrial control applications. In such applications, conventional controllers like P, PI, and PID are being used with the BLDC servomotor drive control systems to achieve satisfactory transient and steady-state responses. However, the major problem associated with the conventional PID controller is that the tuned gain parameters obtained for such BLDC servomotor drive control systems do not yield better transient and steady-state responses under different operating conditions such as parameter variations, load disturbances, etc. In this paper, design and implementation of fuzzy controller is presented and its performance is compared with PID controller to show its capability to track the error and usefulness of fuzzy controller in control applications.
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    System Design and Implementation of UCF-MANUS—An Intelligent Assistive Robotic Manipulator (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
    Details
    Publication Date: 2014-01-22
    Description: This paper reports on the system design for integrating the various processes needed for end-to-end implementation of a smart assistive robotic manipulator. Specifically, progress is reported in the empowerment of the UCF-MANUS system with a suite of sensory, computational, and multimodal interface capabilities so that its autonomy can be made accessible to users with a wide range of disabilities. Laboratory experiments are reported to demonstrate the ability of the system prototype to successfully and efficiently complete object retrieval tasks. Benchmarking of the impact of the various interface modalities on user performance is performed via empirical studies with healthy subjects operating the robot in a simulated instrumental activities of daily living tasks setup. It is seen through a analysis of the collected quantitative data that the prototype is interface neutral and shows robustness to variations in the tasks and the environment. It is also seen that the prototype autonomous system is quantitatively superior to Cartesian control for all tested tasks under a “number of commands” metric, however, under a “time to task completion” metric, the system is seen to be superior for “hard” tasks but not for “easy” tasks.
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    Robust Visual Tracking of Robotic Forceps Under a Microscope Using Kinematic Data Fusion (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: Forceps tracking is an important element of high-level surgical assistance such as visual servoing and motion analysis. This paper describes a robust, efficient tracking algorithm capable of estimating the forceps tip position in an image space by fusing visual tracking data with kinematic information. In visual tracking, the full-state parameters of forceps are estimated using the projective contour models of a 3-D CAD model of the forceps. The likelihood of the contour model is measured using the distance transformation to enable fast calculation, and the particle filter estimates the full state of the forceps. For more robust tracking, the result data obtained from visual tracking are combined with kinematic data that are obtained by forward kinematics and hand–eye transformation. The fusion of visual and kinematic tracking data is performed using an adaptive Kalman filter, and the fused tracking enables the reinitialization of visual tracking parameters when a failure occurs. Experimental results indicate that the proposed method is accurate and robust to image noise, and forceps tracking was successfully carried out even when the forceps was out of view.
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    Compensating for ZOH-Induced Residual Vibrations in Head-Positioning Control of Hard Disk Drives (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: In a hard disk drive, residual vibrations induced by a zero-order-hold may lead to destruction of user data. Therefore, we developed a control method that can reduce such residual vibrations in the head-positioning control system of a hard disk drive. This study is based on a shock response spectrum (SRS) analysis that handles the transient-state characteristics of mechanical resonances. The control method uses multirate notch filters that modify the acceleration input signals beyond the Nyquist frequency. The results of the SRS analyses showed that the multirate notch filter was able to decrease the amplitude of residual vibrations caused by the mechanical resonances around the sampling frequency. Simulation and experimental results for a track-seeking control in a hard disk drive demonstrated the validity of the proposed method.
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    Wet Adhesion Inspired Bionic Climbing Robot (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: Arthropods like stick insects have remarkable locomotion performance to climb vertical surfaces with their wet adhesion pads. This paper focuses on the development of a novel wet adhesion pad for wall-climbing robots that can scale walls. According to the morphology of insects’ pads, mechanism of wet adhesive is analyzed. A novel wet adhesive pad with microstructure based on combining electroforming process with soft lithography is explored. Characteristic test results show that microstructures on the surface of pads fabricated by the proposed technique can improve the wet adhesive ability effectively. The design, manufacture, and test of a hexapod climbing robot prototype are also discussed. Experimental results show that the climbing ability of the robot with the pads is exceptional; the robot can climb up to more than 80 $^{circ}$ sloped surface and stick to the vertical surface statically.
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    An Energy-Efficient Hopping Robot Based on Free Vibration of a Curved Beam (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper explores a design strategy of hopping robots, which makes use of free vibration of an elastic curved beam. In this strategy, the leg structure consists of a specifically shaped elastic curved beam and a small rotating mass that induces free vibration of the entire robot body. Although we expect to improve energy efficiency of locomotion by exploiting the mechanical dynamics, it is not trivial to take advantage of the coupled dynamics between actuation and mechanical structures for the purpose of locomotion. From this perspective, this paper explains the basic design principles through modeling, simulation, and experiments of a minimalistic hopping robot platform. More specifically, we show how to design elastic curved beams for stable hopping locomotion and the control method by using unconventional actuation. In addition, we also analyze the proposed design strategy in terms of energy efficiency and discuss how it can be applied to the other forms of legged robot locomotion.
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    Controlling the Trajectory of a Flexible Ultrathin Endoscope for Fully Automated Bladder Surveillance (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: During cystoscopy, the urologist manually steers a cyst scope inside a patient's bladder to visually inspect the inner surface. Cystoscopies are performed as part of surveillance for bladder cancer, making it the most expensive cancer to treat over a patient's lifetime. An automated bladder scanning system has been devised to reduce workload and cost by relieving the urologist from performing surveillance. Presented here is a proof-of-concept apparatus that controls the motion of a miniature flexible endoscope. Image-based feedback is used to adjust the endoscope's movement so that captured images overlap with one another, ensuring that the entire inner surface of the bladder is imaged. Within a bladder phantom, the apparatus adaptively created and followed a spherical scan pattern comprised of 13 individual latitudes and 508 captured images, while accepting between 60% and 90% image overlap between adjacent images. The elapsed time and number of captured images were sensitive to the apparatus's placement within the phantom and the acceptable image overlap percentage range. A mosaic of captured images was generated to validate comprehensive surveillance. Overall, a robotically controlled endoscope used in conjunction with image-based feedback may permit fully automated and comprehensive bladder surveillance to be conducted without direct clinician oversight.
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    Pseudo-Sensorless High-Performance Bilateral Teleoperation by Sliding-Mode Control and FPGA (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper proposes a pseudo-sensorless implementation of scaled bilateral teleoperation. It is based on Hall effect sensors that are built within the motor housing. The proposed implementation requires no external sensor that can deteriorate system dynamics and performance. The integrated sensors have been used both for position measurement and external force estimation that are necessary in high-performance bilateral teleoperation. Nevertheless, system perturbation dynamics may always appear in a practical mechatronic system. Therefore, the chattering-free sliding-mode control algorithm is applied that ensures robustness toward the disturbances, and yet is easy to implement. The data acquisition algorithms as well as the control algorithm are implemented by field-programmable gate array (FPGA) in order to provide high control rate that can further increase robustness required for haptic fidelity of the system for scaled teleoperation. The applied algorithms along with the FGPA implementation were validated by the 2-DoF experimental system. It has been shown that the proposed pseudo-sensorless implementation by FPGA provides high bilateral teleoperation performance.
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    A Long-Stroke Nanopositioning Control System of the Coplanar Stage (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: With the continuing trend toward device miniaturization in many engineering and scientific fields, the need to accomplish highly precise measurements at the micro- or nanoscale has emerged as a critical concern. This paper presents a high-precision motion control system for the nanopositioning of a coplanar $Xhbox{--}Y$ stage driven by two commercial ultrasonic motors. The motor drive provides three main driving modes, namely ac, Gate, and dc, for millimeter, micrometer, and nanometer displacements, respectively. The displacement of each axis stage is sensed using a linear diffraction grating interferometer (LDGI) with a nanometer resolution. To compensate for the effects of the variable friction force during stage motion, the gains of the proportional–integral–derivative controller used to regulate the stage motion are tuned adaptively by a back propagation neural network (BPNN) based on the feedback signals provided by the LDGI. Furthermore, to obtain a high-accuracy positional motion, the error compensation strategy is implemented to eliminate the systematic errors of the stage with error budget. The error budget is obtained by positioning error calibration using a laser interferometer, which optical axis is detected by a quadrant photodetector (QPD) to ensure no cosine error. The positioning accuracy of the proposed system is evaluated by performing a series of contouring experiments. The results demonstrate that the system achieves a nanometer level of accuracy and resolution and is, therefore, a suitable solution for micro-coordinate measuring machine, microlithography, and micromachining applications.
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    A Pneumatically Actuated Quadrupedal Walking Robot (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper describes the mechanical design and control of a pneumatic quadrupedal robot. Additionally, the authors propose a method of joint control that combines stance/swing gain scheduling with open-loop damping, the combination of which provides stable joint level control, without the oscillatory behavior associated with pneumatically actuated walking robots. A set of joint trajectories are described to provide stable walking. The joint trajectories and joint-level controllers are implemented on the pneumatic quadruped and experimentally shown to provide stable walking without significant (unwanted) oscillations of the body or legs. Further, the robot's normalized speed and payload capacity are experimentally characterized. The robot's performance in these metrics is shown to be highly competitive within the published literature.
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    IEEE/ASME Transactions on Mechatronics information for authors (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
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    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
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    High-Sampling Rate Dynamic Inversion—Filter Realization and Applications in Digital Control (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper presents a stable inversion of nonminimum phase systems with highly efficient computation for high-sampling rate applications. The stable filter that inverts the dynamics of a nonminimum system is based on cascading a stable pole-zero cancellation infinite impulse response (IIR) filter with a high-order finite impulse response (FIR) filter which inverts the unstable zero dynamics. The high-order FIR filter is realized based on efficient IIR filter implementation first introduced by Powell and Chau then later modified by Kurosu. As a demonstrative example, the inversion filters are applied to feedforward tracking and repetitive control algorithms and realized by a field programmable gate array. The controllers are implemented at 100-kHz sampling rate to control the motion of a 4 degrees-of-freedom magnetically levitated shaft in experiment.
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    Mechanochemical synthesis and giant dielectric properties of CaCu 3 Ti 4 O 12 (2014)
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    Publication Date: 2014-01-12
    Description: CaCu 3 Ti 4 O 12 powder has been synthesized by mechanochemical milling (C-m) and solid-state reaction (C-ssr) techniques. C-m powder has a grain size of ~24 nm as determined from X-ray diffraction and FE-SEM measurements. The grain size of C-m ceramics has increased to 20 μm compared to a size of 3 μm for C-ssr ceramics after sintering at 1,050 °C for 10 h. Giant dielectric constant was observed in both ceramics with that of C-m larger than that of C-ssr. Impedance results show that the grain conductivity of C-m is more than two orders of magnitude lower than that of C-ssr, whereas its grain boundary conductivity is larger than that of C-ssr. These results are supported by the EDX results that show Cu-enriched grain boundaries in C-m ceramics.
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    On the generation of bulk microdefects in phosphorus-diffused monocrystalline silicon solar wafers after a high-thermal treatment studied by X-ray topography (2014)
    Springer
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    Publication Date: 2014-01-12
    Description: Oxygen is the most important impurity in free dislocation Czochralski silicon single crystals incorporated interstitially during the growth. The knowledge of oxygen behavior after thermal processes is of great technological importance, since different kinds of bulk microdefects such us SiO 2 precipitates, dislocation loops and stacking faults can be generated. In monocrystalline silicon solar cell manufacturing fabrication, there are several high-thermal treatments. The first is the diffusion process at 850–900 °C. Three different kinds of phosphorus diffusion wafers, standard PO 3 Cl liquid, spray-on and screen printing, were comparatively studied by X-ray topography showing that phosphorus diffusion improves the crystal quality by a gettering process whose best efficiency is in PO 3 Cl-diffused wafers. Later, another fabrication high-thermal step is for instance the rear surface passivation taking place at temperatures from 800 to 1,050 °C. For this reason, it is important to study how a high-thermal treatment at 1,000 °C affects the different phosphorus-diffused wafers mentioned above. To evaluate and characterize the possible defects induced by the oxygen precipitation, X-ray topography has been employed. Results show that annealed wafers are not perfect crystals; the oxygen precipitation induces the generation of bulk microdefects whose kind, size and density depend on the diffusion method employed. In PO 3 Cl and spray-on diffused wafers, retardation in the oxygen precipitation process takes place after annealing, while in screen printing this process is recovered and a kind of mixed defects between dislocation loops and platelet precipitates is generated.
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    Characterization of hydrophobic, oxidized porous silicon layer formed by anodic etching of n + -type silicon surface in a HF:C 2 H 5 OH:HCl:H (2014)
    Springer
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    Publication Date: 2014-01-18
    Description: Porous silicon (PS) has been prepared in the dark by anodic etching of n + -type (111) silicon substrate in a HF:HCl:C 2 H 5 OH:H 2 O 2 :H 2 O electrolyte. The processed PS layer is characterized by means of photoluminescence (PL) spectroscopy, scanning electron microscope (SEM), water contact angle (CA) measurements, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and micro-Raman scattering. The CA of fresh PS layer is found to be ~142°. On aging at ambient conditions, the CA decreases gently to reach ~133° after 3 month, and then it is stabilized for a prolonged time of aging. The visible PL emission from the PS layer also exhibits a good stability against aging time. The FTIR and XPS measurements and analysis show that the stable aged PS layer has rather SiO 2 -rich surface. The micro/nanostructure nature of the PS layer is revealed from SEM and micro-Raman results and correlated to CA results. Stable hydrophobic surface of oxidized PS layer is attractive for bio-applications. The efficiency of the produced PS layers as an entrapping template for specific immobilization of IgG2a antibody via physical absorption process is demonstrated.
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    Electrical properties and conduction mechanism of an organic-modified Au/NiPc/n-InP Schottky barrier diode (2014)
    Springer
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    Publication Date: 2014-01-18
    Description: The effect of nickel phthalocyanine (NiPc) organic interlayer on the electronic parameters of Au/n-InP Schottky contacts has been investigated using current–voltage ( I – V ) and capacitance–voltage ( C – V ) measurements. Measurements showed that the barrier heights and ideality factors are 0.58 eV ( I – V ), 0.69 eV( C – V ) and 1.32 for Au/n-InP Schottky contact and 0.80 eV ( I – V ), 1.12 eV ( C – V ) and 1.73 for Au/NiPc/n-InP Schottky contact, respectively. Experimental results show that the interfacial layer of NiPc increases the effective barrier height by the influence of the space charge region of the Au/n-InP Schottky junction. Further, Cheung’s and modified Norde functions are used to extract the barrier height, series resistance and ideality factors. The discrepancy between barrier heights estimated from I – V to C – V methods is also explained. Moreover, the energy distribution of interface state density is determined from the forward bias I – V data. Results show that the interface states and series resistance play an important role on electrical properties of the structures studied. The reverse leakage current conduction mechanism is investigated. Results reveal that the Schottky conduction mechanism is found to be dominant in the Au/n-InP Schottky contact. However, in the case of Au/NiPc/n-InP Schottky contact, the Schottky conduction mechanism is found to be dominant in the higher bias region, while Poole–Frenkel conduction is found to be dominant in the lower bias region.
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    Laser-induced periodic surface structures on polymers for formation of gold nanowires and activation of human cells (2014)
    Springer
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    Publication Date: 2014-01-19
    Description: Frequently observed coherent structures in laser-surface processing are ripples, also denoted as laser-induced periodic surface structures (LIPSS). For polyethylene terephthalate (PET) and polystyrene (PS), LIPSS can be induced by irradiation with linearly polarized ns-pulsed UV laser light. Under an angle of incidence of θ , their lateral period is close to the laser wavelength λ divided by ( n eff  − sin θ ). Here, n eff is the effective refractive index which is 1.32 and 1.23 for PET and PS, respectively. We describe potential applications of LIPSS for alignment and activation of human cells cultivated on polymer substrates, as well as for formation of separated gold nanowires which show pronounced surface plasmon resonances, e.g., at 775 nm for PET.
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    Degradation sources of CdTe thin film PV: CdCl 2 residue and shunting pinholes (2014)
    Springer
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    Publication Date: 2014-01-21
    Description: The present work considers two observable phenomena through the experimental fabrication and electrical characterization of the rf-sputtered CdS/CdTe thin film solar cells that extremely reduce the overall conversion efficiency of the device: CdCl 2 residue on the surface of the semiconductor and shunting pinholes. The former happens through nonuniform treatment of the As-deposited solar cells before annealing at high temperature and the latter occurs by shunting pinholes when the cell surface is shunted by defects, wire-like pathways or scratches on the metallic back contact caused from the external contacts. Such physical problems may be quite common in the experimental activities and reduce the performance down to 4–5 % which leads to dismantle the device despite its precise fabrication. We present our electrical characterization on the samples that received wet CdCl 2 surface treatment (uniform or nonuniform) and are damaged by the pinholes.
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    A New Actuator With Adjustable Stiffness Based on a Variable Ratio Lever Mechanism (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper presents the actuator with adjustable stiffness (AwAS-II), an enhanced version of the original realization AwAS. This new variable stiffness actuator significantly differs from its predecessor on the mechanism used for the stiffness regulation. While AwAS tunes the stiffness by regulating the position of the compliant elements along the lever arm, AwAS-II changes the position of the lever's pivot point. As a result of the new principle, AwAS-II can change the stiffness in a much broader range (from zero to infinity) even by using softer springs and shorter lever arm, compared to AwAS. This makes the setup of AwAS-II more compact and lighter and improves the stiffness regulation response. To evaluate the aptitude of the fast stiffness adjustment, experiments on reproducing the stiffness profile of the human ankle during the stance phase of a normal walking gait are conducted. Results indicate that AwAS-II is capable of reproducing an interpolated stiffness profile of the ankle while providing a net positive work and thus a sufficient amount of energy as required for the toe-off.
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    Design, Development, and Evaluation of a Pinch–Grasp Haptic Interface (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: Interaction with virtual or teleoperated environments requires contact with objects on a multipoint level. We describe the design of a pinch–grasp hand interface device for use as a grasping mechanism to complement haptic interfaces. To preserve a suitable level of transparency for human–computer interaction, this novel interface is designed for high-resolution contact forces, while centered around a lightweight structure. This functionality renders the device scalable and adaptable to a wide range of haptic interface structures and force level requirements. We present an optimal configuration for a pinch–grasp interface, which produces bidirectional forces to an operator’s fingers and a rotational force to the wrist through a cable drive system. The device is characterized for use on a commercial haptic interface through demonstration of sustained peak performance and also workspace utilization. The dynamic performance of the pinch–grasp interface is experimentally determined, and the frequency response is identified to illustrate its contact force resolution.
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    Can DC Motors Directly Drive Flapping Wings at High Frequency and Large Wing Strokes? (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper proposes and experimentally validates a method for driving flapping wings at large wing strokes and high frequencies with a DC motor, based on direct, elastic transmission. The DC motor undergoes reciprocating, rather than rotary, motion avoiding the use of nonlinear transmissions such as slider-crank mechanisms. This is key to compact, easy to fabricate, power efficient, and controllable flapping mechanisms. First, an appropriate motor based on maximum power transfer arguments is selected. Then, a flapping mechanism is prototyped and its experimental performance is compared with simulations, which take into account the full dynamics of the system. Despite inherent nonlinearities due to the aerodynamic damping, the linearity of the direct, elastic transmission allows one to fully exploit resonance. This benefit is best captured by the dynamic efficiency, close to 90% at larger wing strokes in both experimental data and simulations. We finally show a compact flapping mechanism implementation with independent flapping motion control for the two wings, which could be used for future autonomous micro-aerial vehicles.
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    Design and Development of the Cable Actuated Finger Exoskeleton for Hand Rehabilitation Following Stroke (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: Finger impairment following stroke results in significant deficits in hand manipulation and the performance of everyday tasks. While recent advances in rehabilitation robotics have shown promise for facilitating functional improvement, it remains unclear how best to employ these devices to maximize benefits. Current devices for the hand, however, lack the capacity to fully explore the space of possible training paradigms. Particularly, they cannot provide the independent joint control and levels of velocity and torque required. To fill this need, we have developed a prototype for one digit, the cable actuated finger exoskeleton (CAFE), a three-degree-of-freedom robotic exoskeleton for the index finger. This paper presents the design and development of the CAFE, with performance testing results.
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    Complementary Observer for Body Segments Motion Capturing by Inertial and Magnetic Sensors (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper presents a viable quaternion-based complementary observer (CO) that is designed for rigid body attitude estimation. We claim that this approach is an alternative one to overcome the limitations of the extended Kalman filter. The CO processes data from a small inertial/magnetic sensor module containing triaxial angular rate sensors, accelerometers, and magnetometers, without resorting to GPS data. The proposed algorithm incorporates a motion kinematic model and adopts a two-layer filter architecture. In the latter, the Levenberg Marquardt algorithm preprocesses acceleration and local magnetic field measurements, to produce what will be called the system's output. The system's output together with the angular rate measurements will become measurement signals for the CO. In this way, the overall CO design is greatly simplified. The efficiency of the CO is experimentally investigated through an industrial robot and a commercial IMU during human segment motion exercises. These results are promising for human motion applications, in particular future ambulatory monitoring.
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    An Adaptive Wearable Parallel Robot for the Treatment of Ankle Injuries (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper presents the development of a novel adaptive wearable ankle robot for the treatments of ankle sprain through physical rehabilitation. The ankle robot has a bioinspired design, devised after a careful study of the improvement opportunities in the existing ankle robots. Robot design is adaptable to subjects of varying physiological abilities and age groups. Ankle robot employs lightweight but powerful pneumatic muscle actuators (PMA) which mimics skeletal muscles in actuation. To address nonlinear characteristics of PMA, a fuzzy-based disturbance observer (FBDO) has been developed. Another instance of an adaptive fuzzy logic controller based on Mamdani inference has been developed and appended with the FBDO to compensate for the transient nature of the PMA. With the proposed control scheme, it is possible to simultaneously control four parallel actuators of the ankle robot and achieve three rotational degrees of freedom. To evaluate the robot design, the disturbance observer, and the adaptive fuzzy logic controller, experiments were performed. The ankle robot was used by a neurologically intact subject. The robot–human interaction was kept as active–passive while the robot was operated on predefined trajectories commonly adopted by the therapists. Trajectory tracking results are reported in the presence of an unpredicted human user intervention, use of compliant and nonlinear actuators, and parallel kinematic structure of the ankle robot.
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    Integrating the Microsoft Kinect With Simulink: Real-Time Object Tracking Example (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: The introduction of low-cost, relatively high-resolution 3-D sensing systems, like the Microsoft Kinect, has considerable potential in autonomous system applications. One of the impediments to wider Kinect application development is that the available Kinect drivers define C language interfaces. To help fully realize the Kinect’s potential, the aims of this paper are 1) to develop a “VU-Kinect ” block which provides easy access to the sensor’s camera and depth image streams, and which enables them to be incorporated seamlessly within a higher level, Simulink-based, image-processing and real-time control strategy; 2) to address implementation issues associated with the Kinect, such as sensor calibration; and 3) to show the utility of both the VU-Kinect block and the Kinect itself through a simple 3-D object tracking example.
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    Implementing Flexible and Fast Turning Maneuvers of a Multijoint Robotic Fish (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper focuses mainly on the control issues of replicating fast C-start maneuvers commonly found in fish propelled by their bodies and/or caudal fins. To generate an escape maneuver that combines a high degree of flexibility and precision, major factors related to the caudal fins, the moving joints, and the used motors are explored. Specifically, the turning rate is maximized by finely designing the preparatory and propulsive stages, while the relatively precise turning angle is achieved by a closed-loop control strategy in the propulsive and variable stages. Different types of C-starts are extensively implemented and compared by using a four-joint robotic fish. The latest results obtained show that the robotic fish is able to execute C-starts flexibly with a turning angle of up to 213 $^circ$ , a top turning rate of approximately 670 $^circ$ /s measured by the onboard gyroscope. Meanwhile, an upper limit of turning precision of less than 10 $^circ$ is achieved.
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    Investigation of the crystallinity, structural, and optical properties in hydrotreating of Li–W co-doped ZnO thin films (2014)
    Springer
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    Publication Date: 2014-01-22
    Description: The hydrotreated Li–W co-doped ZnO (LWZO:H) thin films was prepared on quartz glass substrates by RF magnetron sputtering at substrate temperature 100 °C with varied hydrogen flow ratios. The X-ray diffraction spectra indicated that the hydrotreating Li–W co-doped ZnO films showed a preferred orientation toward the c -axis. The chemical compositions of all samples were confirmed by X-ray photoelectron spectroscopy, which clearly showed the existence of W as a doping element into ZnO crystal lattice. The surface morphology of LWZO:H thin films changed with the increasing R value can clearly be seen. The average transmittance of the films was found to be almost 85 % for the wavelength range of 400–1,200 nm. Meanwhile, the optical band gap increase of the films may be attributed to the band Burstein–Moss effect.
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    Post-black etching on emitter to improve performance of multi-scale texture silicon solar cells (2014)
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    Publication Date: 2014-01-22
    Description: A simple, low-cost, post-black etching process atop the random pyramidal emitter has been proposed and investigated. The multi-scale texture is achieved by combining nanoporous layer formed by the post-black etching with micron-scale pyramid texture. Compared to the pre-black etched Si solar cells, our experiments clearly show the advantage of post-black etched texturing: it enables high blue response and improved conversion efficiency. As a result, the enhancement of 7.1 mA/cm 2 on the short-circuit current density and improvement of 31 % in the conversion efficiency have been reached.
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    Bipolar Piezoelectric Buckling Actuators (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: A nonlinear piezoelectric amplification mechanism utilizing structural buckling is presented, and its static and dynamic properties are measured and analyzed. Buckling is a pronounced nonlinear effect that occurs at a structurally singular point. A small piezoelectric displacement on the order of 10 μm results in a large buckling displacement on the order of millimeter. Furthermore, the usable stroke is doubled if both sides of the singular point can be reached resulting in bipolar motion. Despite the large gain, buckling is an erratic, singular phenomenon; the side on which deflection will occur is unpredictable. In this paper, multiple design concepts are presented for regulating the buckling direction as well as for extending its usable stroke to bipolar motion. Nonlinear force–displacement relationships are modeled and measured. Nonlinear dynamic analysis using phase planes reveals that the buckling actuator can generate bipolar motion above a specific amplitude. Below this amplitude, it generates only monopolar oscillation. The proposed design concepts are implemented on monolithic flexure mechanisms, and prototype buckling actuators are tested to verify the concepts. Experiments show promising results: 20 N of peak-to-peak output force, and 6.2 mm of bipolar displacement generated by piezoelectric actuators with free displacement of 42 μm.
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    Electromechanical Piezoelectric Power Harvester Frequency Response Modeling Using Closed-Form Boundary Value Methods (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: The conversion of mechanical vibration to electrical energy has shown great promise for extending battery life of smart sensor wireless devices for various engineering applications. This paper presents novel analytical models of a piezoelectric bimorph, using the closed-form boundary value (CFBV) method, for predicting the electromechanical power harvester frequency response. The derivations of the coupled electromechanical dynamic response of the transverse-longitudinal (CEDRTL) form based on the CFBV method were developed using the reduced strong form method of the Hamiltonian principle. The equations from CEDRTL can be reduced to give the coupled electromechanical dynamic response of the transverse (CEDRT) form. The electromechanical frequency response functions with variable load resistance were also given in detail using Laplace transformation. The two theoretical studies are compared together and validated with an experimental study. For some cases, when the load resistance approached open circuit, the difference between CEDRTL and CEDRT tended to be more pronounced. Conversely, the CEDRTL and CEDRT models tended to overlap when the load resistance approached short circuit. Nyquist plots are used to demonstrate the shifting frequency and amplitude changes due to variable resistance. Overall, the experimental and CEDRTL model results were very close to each other.
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    Robust Control of a MEMS Probing Device (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: In this paper, a systematic design based on the robust control theory is developed for a microelectromechanical systems nanopositioning/probing device. The device is fabricated on a silicon-on-insulator substrate, and provides decoupled XY motion by using a parallel kinematics mechanism design. Each axis of the device is actuated by linear comb-drives and the corresponding displacements are sensed by separate comb structures. To improve the sensing resolution, the sensing and driving combs are electrically isolated. The nonlinear dynamic model between the actuation voltage and the sensed displacement will increase the complexity of model identification and control design. We circumvent the nonlinear model by redefining the input and output (I/O) signals during the model definition and identification, which results in linear and time-invariant models. A dynamical model of the system is identified through experimental input–output frequency-domain identification. The implemented $H_{bm infty}$ control design achieves a significant improvement over the response speed, where the bandwidths from the closed-loop sensitivity and complementary sensitivity functions, respectively, are 68 and 74 Hz. When compared to open-loop characteristics, enhancement in reliability and repeatability (robustness to uncertainties) as well as noise attenuation (by over 12%) is demonstrated through this design.
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    Novel Force Sensing Approach Employing Prismatic-Tip Optical Fiber Inside an Orthoplanar Spring Structure (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper presents a novel approach to force sensing by integrating prismatic-tip optical fibers with an orthoplanar spring structure. The complete force sensing solution integrating the prismatic-tip-based sensing concept with an orthoplanar spring mechanism to convert applied forces into a well-delivered displacement whose magnitude can be measured using the optical sensing technique is introduced in this paper. To the best knowledge of the authors, this is the first time that such a force sensing concept has been proposed and studied. The compact force sensor prototype described in this paper demonstrates its capability and feasibility in performing force measurement over a range of 0–2.8 N. The combination of the novel concepts of prismatic-tip optical fiber sensing and the planar spring minimizes the thickness of the sensing device. Due to its simple sensing structure, the sensor is easy to manufacture and can be miniaturized for applications in dexterous robotic handling and the aerospace industry. The proposed sensor is made of nonmetallic materials and operates without the need of electronics components in the sensing area; thus, the sensor is not susceptible to electric or magnetic fields.
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    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
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    Regression Methods for Virtual Metrology of Layer Thickness in Chemical Vapor Deposition (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: The quality of wafer production in semiconductor manufacturing cannot always be monitored by a costly physical measurement. Instead of measuring a quantity directly, it can be predicted by a regression method (virtual metrology). In this paper, a survey on regression methods is given to predict average silicon nitride cap layer thickness for the plasma-enhanced chemical vapor deposition dual-layer metal passivation stack process. Process and production equipment fault detection and classification data are used as predictor variables. Various variable sets are compared: one most predictive variable alone, the three most predictive variables, an expert selection, and full set. The following regression methods are compared: simple linear regression, multiple linear regression, partial least square regression, and ridge linear regression utilizing the partial least square estimate algorithm, and support vector regression (SVR). On a test set, SVR outperforms the other methods by a large margin, being more robust toward changes in the production conditions. The method performs better on high-dimensional multivariate input data than on the most predictive variables alone. Process expert knowledge used for a priori variable selection further enhances the performance slightly. The results confirm earlier findings that virtual metrology can benefit from the robustness of SVR, an adaptive generic method that performs well even if no process knowledge is applied. However, the integration of process expertise into the method improves the performance once more.
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    IEEE/ASME Transactions on Mechatronics publication information (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
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    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
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    Kinematic Algorithms and Robust Controller Design for Inertially Stabilized System (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper describes a controller design method for the inertially stabilized system of a tracking radar. Its aim is to track a reference target trajectory with high accuracy while isolating rigid body rotational motions of a host ship. First, we investigate the trajectory generation problem to make the control input for a target tracking on the moving base. Second, dynamic equations of motion are formulated by the spring-mass-damper system to include rigid body dynamics as well as structural flexibility. The unknown parameters of dynamic equations are estimated with experimental input and output data by minimizing a predicted error. Third, mixed sensitivity ${cal H}_infty$ robust controllers are designed to meet the conflict requirements of robustness and performance in the face of uncertainty. Finally, the proposed optimal controllers demonstrate the effectiveness of design methodology, and show high performance by numerical and experimental results.
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    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
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    A Cooperative Heterogeneous Mobile Wireless Mechatronic System (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper describes a framework for controlling a heterogeneous wireless robotic network consisting of aerial and ground vehicles. By use of the term heterogeneous, we imply the synergy of multiple robotic platforms characterized by different dynamics and specialized sensing capabilities. Two main scenarios concerning wireless communications are presented: 1) a decentralized connectivity strategy in which a mesh of ground mobile routers swarms in a cluttered environment maintaining communication constraints based on spring-mass virtual physics, potential functions, and routing optimization and 2) an autonomous communications relay in GPS-denied environments via antenna diversity and extremum-seeking SNR optimization. For both scenarios, we validate the proposed methodologies by numerical simulations and experiments. One important feature of our test bed is that it can be used for both indoor and outdoor operations.
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    Silicon suboxide (SiO x ): laser processing and applications (2014)
    Springer
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    Publication Date: 2014-01-16
    Description: Substoichiometric silicon oxide SiO x with x  〈 2 in form of evaporated or sputtered thin films offers a versatile material basis for laser ablation techniques such as film patterning, laser-induced forward transfer, or laser-induced backside dry etching. Applications in the field of (micro-) optics are favoured strongly by the fact that SiO x can be oxidised to UV-transparent SiO 2 by thermal treatment (furnace or laser annealing). On the other hand, with x  ≈ 1, SiO x exhibits an absorption coefficient of 〉10 5 cm −1 in the deep UV below 250 nm, comparable to strongly absorbing polymers such as polyimide. This enables precise ablation with, e.g., excimer lasers at moderate fluences. For example, UV-transparent diffractive elements or phase masks are made by laser patterning of an appropriate SiO x film and subsequent oxidation to SiO 2 . Modifications of the basic film ablation process lead to novel surface topographies such as blister or cup arrays with potential non-optical applications, e.g., in micro-/nanofluidics.
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    Structural, dielectric and ac conductivity properties of Ni-doped HoFeO 3 before and after gamma irradiation (2014)
    Springer
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    Publication Date: 2014-01-16
    Description: A series of samples of HoFe 1− x Ni x O 3 ( x  = 0.0, 0.1, 0.3) were prepared using the solid-state reaction technique to understand the structural, dielectric and conductivity properties before and after gamma irradiation of accumulated dose of 625 KGy. The X-ray diffraction confirms that all the samples exist in single-phase orthorhombic structure having space group Pbnm. With increasing dopant Ni, the unit cell volume and lattice parameters undergo small change. X-ray analysis show change in the interplanar spacing and full width at half maximum values after gamma irradiation. The Raman spectra of the samples show modifications after gamma irradiation. It can be easily seen that after gamma irradiation intensity, peak width are completely altered by gamma-absorbed dose. Measurement of dielectric loss and dielectric constant at room temperature was performed before and after gamma irradiation in the frequency range of 20 Hz–1 MHz. It is observed that the value of dielectric constant decreases after irradiation. The ac conductivity is estimated from the dielectric constant and loss tangent. Exposure to gamma radiation results in substantial modification in the physical properties of the Ni-doped Ho-based orthoferrites.
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    Laser-induced synthesis of silver nanoparticles and their conjugation with protein (2014)
    Springer
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    Publication Date: 2014-01-16
    Description: Partially oxidized spherical silver nanoparticles (AgNPs) of different size are prepared by pulsed laser ablation in water and directly conjugated to protein S-ovalbumin for the first time and characterized by various optical techniques. UV–Visible spectrum of AgNPs showed localized surface plasmon resonance (LSPR) peak at 396 nm which red shift after protein addition. Further the increased concentration of AgNPs resulted a decrease in intensity and broadening of S-ovalbumin peak (278 nm), which can be related to the formation of protein NPs complex caused by the partial adsorption of S-ovalbumin on the surface of AgNPs. The red shift in LSPR peak of AgNPs after mixing with S-ovalbumin and decrease in protein-characteristic peak with increased silver loading confirmed the formation of protein–AgNPs bioconjugates. The effect of laser fluence on the size of AgNPs and nanoparticle–protein conjugation in the size range 5–38 nm is systematically studied. Raman spectra reveal broken disulphide bonds in the conjugated protein and formation of Ag–S bonds on the nanoparticle surface. Fluorescence spectroscopy showed quenching in fluorescence emission intensity of tryptophan residue of S-ovalbumin due to energy transfer from tryptophan moieties of albumin to AgNPs. Besides this, small blue shift in emission peak is also noticed in presence of AgNPs, which might be due to complex formation between protein and nanoparticles. The binding constant ( K ) and the number of binding sites ( n ) between AgNPs and S-ovalbumin have been found to be 0.006 M −1 and 7.11, respectively.
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    An Instrumented Walking Aid to Assess and Retrain Gait (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: An instrumented walking aid, the iWA system, has been developed to measure kinematic and kinetic properties of walking aid (WA) use and deliver feedback to improve gait. The clinical requirements, technical specification and design of the system are developed through clinical collaboration. The development of the system is described, including hardware components and data analysis used to process the measured data for assessment. The system measurements are validated under controlled laboratory conditions. The iWA system is evaluated in a typical U.K. clinical environment by a participant in a rehabilitation session. The resultant data successfully capture the quality of the participant's WA use and agree with clinical opinion, supporting the efficacy of this approach.
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    A Near-Optimal Sensor Scheduling Strategy for an on–off Controller With an Expensive Sensor (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper describes an efficient method for scheduling an energy-consuming sensor sparingly in combination with an on–off controller, specifically for a finite horizon control problem in which only end states are critical. In certain low-power applications, such as autonomous microrobotics, on–off controllers can be very efficient in operating piezoelectric actuators (and other capacitive actuation schemes) compared to traditional analog and pulsewidth modulation controllers. However, with existing sensing circuitry, sensing at the same frequency as control can be prohibitively expensive, because energy consumption in the sensing circuitry may be comparable or even much higher than energy consumption for actuation. Instead, a method is presented for best scheduling a limited number of sensor measurements and updates to control inputs during a finite horizon on–off control problem, in response to Gaussian disturbances and measurement noise. To simplify the problem, a lower bound for the expected value of a quadratic error function of the end states is found, which permits rapid evaluation of candidate sensor times. When actuator energy consumption is incorporated in the optimization, this produces a numerically efficient near-optimal strategy for determining best measurement times and updates to the control input sequence.
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    Nonlinear Characteristic Output Spectrum for Nonlinear Analysis and Design (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: A systematic method for nonlinear analysis, design, and estimation in the frequency domain is proposed in this study using a new concept—nonlinear characteristic output spectrum (nCOS). The nCOS function is an analytical and explicit expression for the relationship between nonlinear output spectrum and system characteristic parameters of interest (including frequency, nonlinear parameters, and excitation magnitude), and can provide a significant insight into nonlinear analysis and design in the frequency domain. Given some simulation or experimental output data of a nonlinear system, the nCOS function of the system can be accurately determined up to any high nonlinear orders with less simulation trials and computation cost compared with a pure simulation-based study or traditional theoretical computations. Moreover, the method can also be used to accurately determine the linear and nonlinear components in the nonlinear output frequency response (or an output spectrum) of a nonlinear system. These results are definitely of significance to nonlinear analysis and design, nonlinear signal processing, system identification, fault detection, etc., in practice. Examples and case studies including analysis of a nonlinear vehicle suspension system are given to illustrate the results.
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    Niching Genetic Scheme With Bond Graphs for Topology and Parameter Optimization of a Mechatronic System (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper presents a novel multimodal evolutionary optimization algorithm for the complex problem of concurrent and integrated design of a mechatronic system, with the objective of realizing the best topology and the best parameters from a multicriteria viewpoint and with different preferences. The associated search space can be large and complex due to the existence of different classes of configurations, possible topologies, and the parameter values of the elements. The proposed algorithm efficiently explores the search space to find several elite configurations for different preferences, with more detailed competition by incorporating the domain knowledge of experts and considering some criteria that are not included in the course of regular evolutionary optimization. The developed approach consists of a two-loop optimization. For each topology, a genetic algorithm-based optimization is performed to find an elite representative of the topology. The elites will compete with each other to become the best design. A strategy of restricted competition selection is employed in the competition of topologies, with the aim of finding alternative elites from which the one that best satisfies the customer preference may be chosen. The designer may incorporate a higher level competition between elites in order to obtain the global optimum.
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    Advanced Motion Control of Electric Vehicles Based on Robust Lateral Tire Force Control via Active Front Steering (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: This paper presents a new motion control method based on robust lateral tire force control (LTFC) to improve vehicle stability or maneuverability. During cornering, vehicle motion is totally governed by lateral forces acting on tires. Thus, the real-time information on tire forces provides advantages in vehicle motion control. Since the lateral tire force measurements are available by using multisensing hub (MSHub) units which were invented by NSK Ltd., the direct LTFC is realizable via active front steering. In control design, a robust control method, e.g., two degree-of-freedom control (2-DOF) with a disturbance observer, is used for improving the reference tracking performance. Moreover, the stability of the proposed control system is discussed by using small gain theorem. The proposed motion controller is implemented on an experimental in-wheel-motor-driven electric vehicle and its performance and effectiveness are verified by field tests. Finally, practical applications of lateral tire force sensors to vehicle motion control systems are discussed.
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    Performance Tradeoffs Posed by Moving Magnet Actuators in Flexure-Based Nanopositioning (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: Moving magnet actuators (MMAs) are direct-drive, single-phase electromagnetic linear actuators that provide frictionless and backlash-free motion over a range of several millimeters. This paper investigates the feasibility of using MMAs to simultaneously achieve large range, high speed, and high motion quality in flexure-based nanopositioning systems. Component and system level design challenges and associated tradeoffs in meeting the aforementioned nanopositioning performance are discussed and derived. In particular, it is shown that even as the overall size of a traditional MMA is varied, the actuation force remains directly proportional to the square root of the actuator's moving magnet mass and the square root of power consumed. This proportionality constant, identified as the dynamic actuator constant, serves as a figure of merit for MMAs. When an MMA is employed in a flexure-based nanopositioning system, this constant directly impacts the system-level positioning performance in terms of range, resolution, speed, and temperature rise. This quantitative determination highlights the significance of incorporating a thermal management system for heat dissipation, minimizing noise and harmonic distortion in the current driver, and improving the force–stroke uniformity of the actuator. Based on this understanding, a single-axis nanopositioning system, which simultaneously achieves 10 mm range, 4 nm resolution, open-loop natural frequency of 25 Hz, and temperature rise of less than 0.5 °C, is designed, fabricated, and tested. Preliminary controller design and closed-loop operation highlight the potential and limitations of MMAs in large-range, high-speed nanopositioning.
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    Call for papers- focused section on Mechatronics for Intelligent Manufacturing (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
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    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
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    State Recognition of Pedicle Drilling With Force Sensing in a Robotic Spinal Surgical System (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: Spinal orthopedic surgery is one of the typical high-risk surgeries. During the surgery, bone screws need to be inserted into the narrower vertebral pedicles and any failures in the screw-path-drilling process will directly hurt the important nerves and vessels of the patient. In this paper, a robotic spinal surgical system (RSSS) for assisting pedicle screw insertion surgery is proposed. The novel structural configuration of the RSSS can balance the gravity effects of the arms, and the workspace envelope of the RSSS can better fit the requirements of spinal surgery. The procedure of the screw insertion operation with the proposed RSSS is presented. To simulate the hand feel of the surgeon in surgical operations, a real-time force-sensing algorithm is developed for the screw-path-drilling process using a spherical or a twist drill. With the force sensing, five key states, including the initial state, the outer cortical state, the cancellous state, the transitional state, and the inner cortical state, are recognized. In particular, the clear recognition of the transitional zone between the cancellous bone and the inner cortical bone is very important as the drilled screw path ends in this zone. State recognition with force sensing can effectively improve the quality of the screw paths so as to enhance the quality of the spinal surgery. Experiments were carried out to verify the state recognition effects of the pedicle drilling process with force sensing.
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    A New Wheelchair Ergometer Designed as an Admittance-Controlled Haptic Robot (2014)
    Institute of Electrical and Electronics Engineers (IEEE) ; American Society of Mechanical Engineers (ASME)
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    Publication Date: 2014-01-22
    Description: Wheelchair ergometers aim to simulate the propulsion of a wheelchair in a controlled laboratory setup. One drawback of current ergometers is that the simulated wheelchair is always modeled as a simple unidimensional mass and friction, which do not allow a correct simulation of turning maneuvers. In this paper, we present a new design for a wheelchair ergometer based on haptic robotics. This ergometer allows us to simulate any linear or nonlinear model of the wheelchair–user system in real time, including models that implement turning maneuvers. The presented prototype was validated experimentally. The rear wheels of the ergometer match the rear wheels’ velocities of the simulated wheelchair with a root-mean-square error of 0.9 %. Therefore, the ergometer’s accuracy is mainly bounded by the accuracy of the wheelchair–user model, which means that future improvements of the wheelchair–user model will be directly reflected by the ergometer. The conditions for stability were also evaluated. A minimal simulated mass of 18 kg and a minimal simulated moment of inertia of 1 kg $cdot$ m $^2$ are needed. These requirements are encountered by any wheelchair–user combination.
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    Comparative theoretical analysis of continuous wave laser cutting of metals at 1 and 10 μm wavelength (2014)
    Springer
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    Publication Date: 2014-01-23
    Description: We present a derivation and, based on it, an extension of a model originally proposed by V.G. Niziev to describe continuous wave laser cutting of metals. Starting from a local energy balance and by incorporating heat removal through heat conduction to the bulk material, we find a differential equation for the cutting profile. This equation is solved numerically and yields, besides the cutting profiles, the maximum cutting speed, the absorptivity profiles, and other relevant quantities. Our main goal is to demonstrate the model’s capability to explain some of the experimentally observed differences between laser cutting at around 1 and 10 μm wavelengths. To compare our numerical results to experimental observations, we perform simulations for exactly the same material and laser beam parameters as those used in a recent comparative experimental study. Generally, we find good agreement between theoretical and experimental results and show that the main differences between laser cutting with 1- and 10-μm beams arise from the different absorptivity profiles and absorbed intensities. Especially the latter suggests that the energy transfer, and thus the laser cutting process, is more efficient in the case of laser cutting with 1-μm beams.
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    Dynamics of femtosecond laser-produced plasma ions (2014)
    Springer
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    Publication Date: 2014-01-24
    Description: We investigated the ion laser-produced plasma plume generated during ultrafast laser ablation of copper and silicon targets in high vacuum. The ablation plasma was induced by ≈50 fs, 800 nm Ti:Sa laser pulses irradiating the target surface at an angle of 45°. An ion probe was used to investigate the time-of-flight profiles of the emitted ions in a laser fluence range from the ablation threshold up to ≈10 J/cm 2 . The angular distribution of the ion flux and average velocity of the produced ions were studied by moving the ion probe on a circle around the ablation spot. The angular distribution of the ion flux is well described by an adiabatic and isentropic model of expansion of a plume produced by laser ablation of solid targets. The angular distribution of the ion flux narrows as the laser pulse fluence increases. Moreover, the ion average velocity reaches values of several tens of km/s, evidencing the presence of ions with kinetic energy of several hundred eV. Finally, the ion flux energy is confined in a narrow angular region around the target normal.
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    Optimization of transverse electric peak-type metal-clad waveguide sensor using double-negative materials (2014)
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    Publication Date: 2014-03-12
    Description: In a very recent work, a transverse electric peak-type metal-clad waveguide optical sensor was proposed in which a double-negative material (DNM) was used as a guiding layer. The sensor was found to exhibit a considerable angular shift of the reflectance peak for small changes in the refractive index of the analyte, due to the DNM layer. In this work, the optimization of the structure parameters is investigated to find out the most appropriate metal and its optimal thickness. Moreover, the optimal DNM layer parameters corresponding to the highest sensitivity are explored. Our calculations reveal that metals with high absolute value of the real part of the permittivity correspond to sharper peaks. Moreover, as the absolute value of the real part of both ε and μ of the DNM increases, the reflectance peak becomes sharper and the dip following the peak becomes deeper.
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    Pulsed laser deposition of rare-earth-doped gallium lanthanum sulphide chalcogenide glass thin films (2014)
    Springer
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    Publication Date: 2014-03-12
    Description: Amorphous chalcogenide thin films are of high current interest for technological applications as optical storage media or waveguides for photonic integrated circuits. As part of a larger project including fs, ps and ns pulsed laser deposition regimes, Er- and Pr-doped GLS thin films were deposited by ns PLD, and their structural, chemical and optical properties were analyzed by optical and electronic microscopy, stylus profilometry, X-ray diffraction, Raman spectroscopy, time-of-flight secondary ion mass spectrometry (TOF–SIMS), energy-dispersive X-ray spectroscopy, variable-angle spectroscopic ellipsometry and optical transmission. Films deposited at moderate fluence (~4 J/cm 2 ) in UV (266 nm) presented a good surface quality, while exhibiting acceptable composition uniformity and deviations from stoichiometry in line with the literature. Composition and optical properties dependences on the deposition conditions were investigated and discussed with respect to previous studies on similar systems.
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    Antibacterial properties of composite UHMWPE/ $\mathrm {TiO}_{2-{\it x}}$ (2014)
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    Publication Date: 2014-03-12
    Description: Due to the diffusion of severe pathogens, everyday life is exposed to the risks of contracting severe diseases. For this reason, efficient antimicrobial surfaces are of paramount importance. In this work we present the first evidences of a new technique to obtain an antibacterial ultra high molecular weight polyethylene based on a non-stoichiometric, visible light responsive, titanium oxide coating. The coating was obtained through a process in which titanium ions, resulting from laser ablation of a corresponding target, were accelerated and implanted on the samples. The samples were tested against a Staphylococcus aureus strain, in order to assay their antimicrobial efficacy. Results show that this treatment strongly discourages bacterial colonization of the treated surfaces.
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    Investigation of the spontaneous emission rate of perylene dye molecules encapsulated into three-dimensional nanofibers via FLIM method (2014)
    Springer
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    Publication Date: 2014-03-12
    Description: The decay dynamics of perylene dye molecules encapsulated in polymer nanofibers produced by electrospinning of polymethyl methacrylate are investigated using a confocal fluorescence lifetime imaging microscopy technique. Time-resolved experiments show that the fluorescence lifetime of perylene dye molecules is enhanced when the dye molecules are encapsulated in a three-dimensional photonic environment. It is hard to produce a sustainable host with exactly the same dimensions all the time during fabrication to accommodate dye molecules for enhancement of spontaneous emission rate. The electrospinning method allows us to have a control over fiber diameter. It is observed that the wavelength of monomer excitation of perylene dye molecules is too short to cause enhancement within nanofiber photonic environment of 330 nm diameters. However, when these nanofibers are doped with more concentrated perylene, in addition to monomer excitation, an excimer excitation is generated. This causes observation of the Purcell effect in the three-dimensional nanocylindrical photonic fiber geometry.
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    The role of H-plasma on aluminum-induced crystallization of amorphous silicon (2014)
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    Publication Date: 2014-03-12
    Description: We propose a technique to improve and accelerate aluminum-induced crystallization (AIC) by hydrogen plasma. Raman spectroscopy and secondary ion mass spectrometry of crystallized poly-silicon thin films show that hydrogen plasma radicals reduce the crystallization time of AIC. This technique shortens the annealing time from 10 to 4 h and increases the Hall mobility from 22 to 42 cm 2 /V s. The possible mechanism of AIC assisted by hydrogen radicals is also discussed.
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    Improved electrical properties of La 2/3 Ba 1/3 MnO 3 :Ag 0.04 thin films by thermal annealing (2014)
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    Publication Date: 2014-03-12
    Description: La 2/3 Ba 1/3 MnO 3 :Ag 0.04 (LBMO:Ag 0.04 ) thin films were prepared on single crystalline (001)-orientated LaAlO 3 substrates by pulsed laser deposition technique. Thermal annealing with temperatures of 780, 800 and 820 °C has been investigated to improve electrical properties of the films. All the samples are shown along the (00 l ) orientation in rhombohedral structure with $ R\overline{3} c $ space group. With thermal annealing temperature increasing, insulator–metal transition temperature ( T p ) and resistivity at T p ( $ \rho_{{T_{\text{p}} }} $ ) of the epilayer reach optimal value of 288 K and 0.03 Ω·cm, respectively. The electrical properties improvement of the LBMO:Ag 0.04 films is due to an improved film crystallization, oxygen balance and photon scattering suppression. The fitting curves show that the region of ferro-magnetic metallic (FM, T  〈  T p ) is fitted with grain/domain boundary, electron–electron and magnon scattering mechanism, as well as the region of para-magnetic insulating (PI, T  〉  T p ) is fitted with adiabatic small polaron hopping mechanism.
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    Diluted magnetic ferroelectric effect in BaTi 0.9 Hf 0.05 Co 0.05 O 3 ceramic (2014)
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    Publication Date: 2014-03-12
    Description: We report that magnetism, especially ferromagnetism, can be induced in a nonmagnetic ferroelectric oxide such as barium titanate (BaTiO 3 ) with choosing of suitable dopants. High-density polycrystalline sample of BaTi 0.9 Hf 0.05 Co 0.05 O 3 was prepared using solid-state sintering route, and the effect of Co and Hf substitution on structural, magnetic and ferroelectric properties of BaTiO 3 was studied. The magnetic order obtained in the above sample is of intrinsic in nature. Ferromagnetic behavior shown in the BaTi 0.9 Hf 0.05 Co 0.05 O 3 ceramic may be attributed to the effective exchange interactions between oxygen vacancies and Co ions. BaTi 0.9 Hf 0.05 Co 0.05 O 3 ceramic has also shown ferroelectric (lossy type) behavior.
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    High aspect ratio microstructuring of transparent dielectrics using femtosecond laser pulses: method for optimization of the machining throughput (2014)
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    Publication Date: 2014-03-14
    Description: High average power, high repetition rate femtosecond lasers with μJ pulse energies are increasingly used for material processing applications. The unique advantage of material processing with sub-picosecond lasers is efficient, fast and localized energy deposition, which leads to high ablation efficiency and accuracy in nearly all kinds of solid materials. This work focuses on the machining of high aspect ratio structures in transparent dielectrics, in particular chemically strengthened Xensation™ glass from Schott using multi-pass ablative material removal. For machining of high aspect ratio structures, among others needed for cutting applications, a novel method to determine the best relation between kerf width and number of overscans is presented. The importance of this relation for optimization of the machining throughput will be demonstrated.
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    The role of the solvent in the ultrashort laser ablation of palladium target in liquid (2014)
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    Publication Date: 2014-03-15
    Description: In the present study, the pulsed laser ablation in liquid technique was used to produce palladium nanoparticles in acetone and in water. The composition, morphology and oxidation state of the obtained nanoparticles have been characterized by HR-TEM, XPS and XRD techniques. The results evidence that the nature of the solvent influences the physical–chemical properties of the products. In acetone non-aggregate metallic nanoparticles have been obtained, while in water the oxidation of the particles surface is present, as showed by the XPS analysis. Moreover, the particles obtained in water are aggregated and the coalescence effect is evident. The different size distributions of nanoparticles obtained in the two liquids have been interpreted considering the different cavitation bubble dynamics.
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    On the physics of self-organized nanostructure formation upon femtosecond laser ablation (2014)
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    Publication Date: 2014-03-15
    Description: We present new results on femtosecond LIPSS on silicon, fostering the dynamic model of self-organized structure formation. The first set of experiments demonstrates LIPSS formation by irradiation with a femtosecond white light continuum. The ripples are, as usual, perpendicular to the light polarization with a fluence-dependent wavelength between 500 and 700 nm. At higher dose (fluence × number of shots), the LIPSS turn to much coarser structures. The second set of experiments displays the dose dependence of pattern evolution at about threshold fluence. In contrast to the general case of multi-pulse LIPSS, where a strong dependence of the structures on the laser polarization is observed, single-shot exposition of silicon at about the ablation threshold results in a concentric pattern of very regular sub-wavelength ripples following the oval shape of the irradiated spot, without any reference to the laser polarization. When increasing the number of pulses, the usual, typical ripples develop and then coalesce into broader perpendicular structures, interlaced with remnants of the first, finer ripples.
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    Thermal analysis of a part of circuit board card by the photothermal deflection technique (2014)
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    Publication Date: 2014-03-15
    Description: Photothermal deflection which is a non-destructive technique is widely used to study defects in materials. However, high spatial resolution and high sensitivity are required to detect them. To validate the theoretical model that we developed in the case, the sample is immersed in a paraffin oil-filled cell and heated with a laser beam of a diameter less than the dimensions of defects and of power 2 mW instead of several 100 mW power frequently used. Our model was tested on a part of a circuit board card having copper strips spaced periodically and embedded in the resin. The experimental curves of amplitude and phase variations according to displacement of the sample are in good agreement with the corresponding theoretical ones; and their coincidence permit us to deduce several parameters such as the width of the copper and resin strips, their thicknesses and their thermal properties. These comparisons allowed also to detect some anomalies in the structure such as inhomogeneity in the width, the shape and the thicknesses of copper and resins strips.
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    Nano- and femtosecond UV laser pulses to immobilize biomolecules onto surfaces with preferential orientation (2014)
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    Publication Date: 2014-03-15
    Description: By relying on the photonic immobilization technique of antibodies onto surfaces, we realized portable biosensors for light molecules based on the use of quartz crystal microbalances, given the linear dependence of the method on the laser pulse intensity. Here, we compare the quality of the anchoring method when using nanosecond (260 nm, 25 mJ/pulse, 5 ns, 10 Hz rep. rate) and femtosecond (258 nm, 25 μJ/pulse, 150 fs, 10 kHz rep. rate) laser source, delivering the same energy to the sample with the same average power. As a reference, we also tethered untreated antibodies by means of the passive adsorption. The results are striking: When the antibodies are irradiated with the femtosecond pulses, the deposition on the gold plate is much more ordered than in the other two cases. The effects of UV pulses irradiation onto the antibodies are also analyzed by measuring absorption and fluorescence and suggest the occurrence of remarkable degradation when nanosecond pulses are used likely induced by a larger thermal coupling. In view of the high average power required to activate the antibodies for the achievement of the photonic immobilization technique, we conclude that femtosecond rather than nanosecond laser pulses have to be used.
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    The kinetics of the formation of a solid solution in an Ag–Pd polycrystalline film system (2014)
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    Publication Date: 2014-03-15
    Description: The kinetics of homogenization of an Ag–Pd film system with a total thickness of 120 nm and a grain size of 5–10 nm has been studied by means of in situ TEM heating. The film system has been formed by the sequential deposition of components in a vacuum on the substrate at room temperature. It has been shown that diffusion processes are activated, starting from the temperature 453 K, resulting in complete homogenization of the film system at 573 K with preservation of its fine-grained structure. The effective diffusion coefficient in the Ag–Pd system was measured as 10 −17 –10 −18  m 2 /s at 553 K. A possible mechanism of homogenization is discussed.
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    Position-controlled and catalyst-free growth of ZnO nanocrystals by nanoparticle-assisted pulsed laser deposition (2014)
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    Publication Date: 2014-05-04
    Description: We have synthesized ZnO nanocrystals, such as nanowires, nanorods, and nanosheets, using a nanoparticle-assisted pulsed laser deposition (NAPLD) method. Recently, we achieved position-controlled growth of the ZnO nanocrystals by means of a ZnO buffer layer and laser irradiation without any catalyst. The periodic structure was formed on the ZnO buffer layer by multi-beam interference patterning, and then vertically aligned ZnO nanowalls, corresponding to the patterning, were grown on the buffer layer. It was found that the periodic ZnO nanowalls grew along the c -axis direction by X-ray diffraction measurement. The well-aligned ZnO nanowalls are expected to be utilized as building blocks for field emitters and UV LEDs. The proposed technique can be used as one of the effective methods to control the growth position of the ZnO nanocrystals because various structures can be easily fabricated by a laser writing and a spatial light modulator.
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    Saturable absorption and reverse saturable absorption on silver particles with different shapes (2014)
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    Publication Date: 2014-05-07
    Description: Micro/nanostructured silver particles with different shapes (flower, wire, and rod) have been prepared and characterized. All the open aperture z-scan curves of silver microrods and silver nanoflowers present a typical reverse saturable absorption. With the increase of incident intensity, the nonlinear absorption coefficients and the third-order optical susceptibilities ImX (3) of nanoflowers increase, but those of silver microrods decrease. Moreover, the silver nanowires show the conversion from saturable absorption to reverse saturable absorption. There was no definite correlation between incident intensity and nonlinear absorption coefficient ( β ) under the conditions studied herein. And nonlinear optical properties of micro/nanostructured silver particles are dependent on the particle shape in suspensions at 800 nm.
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    Dual metamaterial structures generated from an one-step fabrication using stencil lithography (2014)
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    Publication Date: 2014-05-07
    Description: The flexibility to deposit metallic structures on any substrates without the need of lift-off or etching process are the main reasons for the recent popularity of using stencil lithography for plasmonic applications. In this work, we fabricate nanoholes on a Si 3 N 4 membrane and deposit metal–dielectric layers and such approach allows us to have a perforated fishnet metamaterial structure on the membrane as well as its complementary pillar structure on a quartz substrate. We then studied and compared their optical properties from both experiment and simulation results.
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