A transition of ω-Fe3C → ω'-Fe3C → θ'-Fe3C in Fe-C martensite.

Carbon steel is strong primarily because of carbides with the most well-known one being θ-Fe3C type cementite. However, the formation mechanism of cementite remains unclear. In this study, a new metastable carbide formation mechanism was proposed as ω-Fe3C → ω'-Fe3C → θ'-Fe3C based on the transmission electron microscopy (TEM) observation. Results shown that in quenched high-carbon binary alloys, hexagonal ω-Fe3C fine particles are distributed in the martensite twinning boundary alone, while two metastable carbides (ω' and θ') coexist in the quenched pearlite. These two carbides both possess orthorhombic crystal structure with different lattice parameters (aθ' = aω' = aω = [Formula: see text]aα-Fe = 4.033 Å, bθ' = 2 × bω' = 2 × cω = [Formula: see text]aα-Fe = 4.94 Å, and cθ' = cω' = [Formula: see text]aω = 6.986 Å for aα-Fe = 2.852 Å). The θ' unit cell can be constructed simply by merging two ω' unit cells together along its bω' axis. Thus, the θ' unit cell contains 12 Fe atoms and 4 C atoms, which in turn matches the composition and atomic number of the θ-Fe3C cementite unit cell. The proposed theory in combination with experimental results gives a new insight into the carbide formation mechanism in Fe-C martensite.

Anomalous aortic origin of a coronary artery (AAOCA): A case report.

Anomalous Aortic Origin of a Coronary Artery (AAOCA) is a rare anomaly of the coronary artery with a considerable risk of sudden cardiac death due to ischaemia of the heart. Symptoms may include chest pain on exertion, breathlessness or dizziness. We encountered a case of a 46- year-old female who complained of exertional chest pain with a positive-stress test and subsequently diagnosed with AAOCA through CT angiography (CTA). She successfully underwent a coronary artery bypass graft (CABG) surgery using a saphenous vein graft with uneventful recovery. Right internal mammary artery (RIMA) was not used as it was flimsy and the flow was very poor.

Lath formation mechanisms and twinning as lath martensite substructures in an ultra low-carbon iron alloy.

Lath martensite is the dominant microstructural feature in quenched low-carbon Fe-C alloys. Its formation mechanism is not clear, despite extensive research. The microstructure of an Fe-0.05 C (wt.%) alloy water-quenched at various austenitizing temperatures has been investigated using transmission electron microscopy and a novel lath formation mechanism has been proposed. Body-centered cubic {112}〈111〉-type twin can be retained inside laths in the samples quenched at temperatures from 1050 °C to 1200 °C. The formation mechanism of laths with a twin substructure has been explained based on the twin structure as an initial product of martensitic transformation. A detailed detwinning mechanism in the auto-tempering process has also been discussed, because auto-tempering is inevitable during the quenching of low-carbon Fe-C alloys. The driving force for the detwinning is the instability of ω-Fe(C) particles, which are located only at the twinning boundary region. The twin boundary can move through the ω ↔ bcc transition in which the ω phase region represents the twin boundary.

In situ heating TEM observations on carbide formation and α-Fe recrystallization in twinned martensite.

The microstructural evolution of twinned martensite in water-quenched Fe-1.6 C (wt.%) alloys upon in situ heating was investigated using transmission electron microscopy (TEM). In the as-quenched samples, a high density of a body-centred cubic (bcc) {112} 〈111〉 -type twinning structure exists in the martensite structure. Upon in situ heating to approximately 200-250 °C, carbides (mainly θ-Fe3C cementite) accompanying a detwinning process were observed only in the originally twinned region. The carbides were absent in the originally untwinned (twin-free) region. The experimental results have suggested that the formation of the carbides depends on the twinning-boundary ω-Fe metastable phase, which can be stabilised by interstitial carbon atoms. When the specimens were heated, the twinning-boundary ω-Fe(C) transformed into carbide (mainly θ-Fe3C cementite) particles on the original {112} twinning planes. Further heating resulted in substantial recrystallisation of α-Fe fine particles, which formed immediately after martensite transformation. The results presented here should be helpful in understanding the microstructural evolution of various carbon steels.

Fabrication of Embedded Silver Nanowires on Arbitrary Substrates with Enhanced Stability via Chemisorbed Alkanethiolate.

We propose a versatile yet practical transferring technique to fabricate a high performance and extremely stable silver nanowire (AgNW) transparent electrode on arbitrary substrates. Hydroxylated poly(ethylene glycol) terephthalate (PET) or poly(dimethylsiloxane) (PDMS) deposited with AgNWs was selectively decorated to lower its polar surface energy, so that the AgNWs were easily and efficiently transferred into an epoxy resin (EPR) as a freestanding film (AgNWs-EPR) or onto various substrates. The AgNWs-EPR capped with alkanethiolate monolayers exhibits high conductivity, low roughness, ultraflexibility, and strong corrosion resistance. Using the transferring process, AgNWs-EPR was successfully constructed on rough, adhesive, flimsy, or complex curved substrates, including PET, thin optically clear adhesive, papers, a beaker, convex spherical PDMS, and leaves. A flexible touch panel enabling multitouch and a curved transparent heater on a beaker were first fabricated by using the composite film. These demonstrations suggest that the proposed technique for AgNWs is a promising strategy toward the next generation of flexible/portable/wearable electronics.

Polychromatic SSVEP stimuli with subtle flickering adapted to brain-display interactions.

OBJECTIVE: Interactive displays armed with natural user interfaces (NUIs) will likely lead the next breakthrough in consumer electronics, and brain-computer interfaces (BCIs) are often regarded as the ultimate NUI-enabling machines to respond to human emotions and mental states. Steady-state visual evoked potentials (SSVEPs) are a commonly used BCI modality due to the ease of detection and high information transfer rates. However, the presence of flickering stimuli may cause user discomfort and can even induce migraines and seizures. With the aim of designing visual stimuli that can be embedded into video images, this study developed a novel approach to induce detectable SSVEPs using a composition of red/green/blue flickering lights. APPROACH: Based on the opponent theory of colour vision, this study used 32 Hz/40 Hz rectangular red-green or red-blue LED light pulses with a 50% duty cycle, balanced/equal luminance and 0°/180° phase shifts as the stimulating light sources and tested their efficacy in producing SSVEP responses with high signal-to-noise ratios (SNRs) while reducing the perceived flickering sensation. MAIN RESULTS: The empirical results from ten healthy subjects showed that dual-colour lights flickering at 32 Hz/40 Hz with a 50% duty cycle and 180° phase shift achieved a greater than 90% detection accuracy with little or no flickering sensation. SIGNIFICANCE: As a first step in developing an embedded SSVEP stimulus in commercial displays, this study provides a foundation for developing a combination of three primary colour flickering backlights with adjustable luminance proportions to create a subtle flickering polychromatic light that can elicit SSVEPs at the basic flickering frequency.

Dual layer electrode liquid crystal lens for 2D/3D tunable endoscopy imaging system.

In this paper, we demonstrate a multi-functional liquid-crystal lens (MFLC-lens) based on dual-layer electrode design. Compared with the previous 3D endoscopes, which use double fixed lens capturing, the proposed LC lens is not only switchable between 2D and 3D modes, but also is able to adjust focus in both modes. The diameter of the MFLC-lens is only 1.42mm, which is much smaller than the available 3D endoscopes with double fixed lenses. To achieve the MFLC-lens, a high-resistance layer needs to be coated on the electrode to generate an ideal gradient electric-field distribution, which can induce a lens-like form of LC molecules. The parameters of high-resistive layer are investigated and discussed with an aim to optimize the performance of the MFLC-lens.

Electrically robust silver nanowire patterns transferrable onto various substrates.

We report a facile technique for patterning and transferring silver nanowires (AgNWs) onto various substrates. By employing only UV/O3 and vapor treatment of hexamethyldisilazane (HMDS), we are able to accurately manipulate the surface energy via alternating the terminal groups of a polydimethylsiloxane (PDMS) substrate, so as to assist selective formation and exfoliation of AgNW films. A simple UV/O3 treatment on PDMS enables uniform, well-defined, and highly conductive patterns of AgNWs after spin-coating. A vapor treatment of HMDS lowers the surface energy of the oxidized PDMS so that the patterned AgNWs embedded in an epoxy resin (EPR) are cleanly transferred from the PDMS to the target substrate. It is found that the AgNW-EPR composite on polyethylene glycol terephthalate (PET) exhibits remarkable durability under the bending test, tape test, ultrasonic treatment in water, and immersion of chemical solvents. In addition, we demonstrate that the AgNW-EPR composite work well as conductive patterns on the oxidized PDMS, polyvinyl alcohol (PVA), paper, and curved glass. The facile technique extends the applicability of AgNWs in the field of electronics, and it is potentially applicable to other nanomaterials.

Microchannel Wetting for Controllable Patterning and Alignment of Silver Nanowire with High Resolution.

Patterning and alignment of conductive nanowires are essential for good electrical isolation and high conductivity in various applications. Herein a facile bottom-up, additive technique is developed to pattern and align silver nanowires (AgNWs) by manipulating wetting of dispersions in microchannels. By forming hydrophobic/hydrophilic micropatterns down to 8 µm with fluoropolymer (Cytop) and SiO2, the aqueous AgNW dispersions with the optimized surface tension and viscosity self-assemble into microdroplets and then dry to form anisotropic AgNW networks. The alignment degree characterized by the full width at half-maximum (FWHM) can be well-controlled from 39.8° to 84.1° by changing the width of microchannels. A mechanism is proposed and validated by statistical analysis on AgNW alignment, and a static model is proposed to guide the patterning of general NWs. The alignment reduced well the electrical resistivity of AgNW networks by a factor of 5 because of the formation of efficient percolation path for carrier conduction.

Light extraction from electroluminescent devices using micro-rod array embedded within glass substrate.

The total internal reflection (TIR) effect in conventional electroluminescent devices causes a large amount of light energy trapped in the devices and result in heat energy that adversely affects the performance of the device. In order to enhance the light out-coupling efficiency without sacrificing the electrical properties, a micro-rod array (MRA) structure fabricated by a femtosecond laser was demonstrated. Green, blue, and red organic light-emitting diodes were employed to verify the effect of the proposed method, which increases out-coupling efficiencies by a factor of 1.9, 1.7, and 1.82, respectively, compared with conventional devices. This highly effective method is compatible with current device fabrication processes and is applicable to full-color electroluminescent devices.

Switchable viewing angle display with a compact directional backlight and striped diffuser.

A compact high-directionality backlight module combined with a striped diffuser is proposed to achieve an adjustable viewing angle for eco-display. The micro-prisms on the compact light guide plate guide the emitting rays to the normal viewing angle, whereas a set of striped diffusers scatter the rays to a wide viewing angle. View cones of ± 10° / ± 55° were obtained for narrow/wide viewing modes with 88% / 85% uniformity of spatial luminance, respectively. Compared with the conventional backlight, the optical efficiencies were increased by factors of 1.47 and 1.38 in narrow and wide viewing modes, respectively. In addition, only 5% of power consumption was needed when the backlight worked in private narrow viewing mode to maintain the same luminance as that of a conventional backlight.

Dynamic integral imaging display with electrically moving array lenslet technique using liquid crystal lens.

Integral imaging (InIm) has been widely investigated for three-dimensional (3-D) display applications. Aliasing due to the lenslet arrays is one of the limitations of InIm displays. In this paper, we propose a dynamic InIm display using electrically movable liquid crystal (LC) lens array to implement the moving array lenslet technique (MALT) and to eliminate the multifacet the 3-D images. The improvement of the viewing quality of dynamic InIm display is experimentally verified.

Hexagonal liquid crystal lens array for 3D endoscopy.

A liquid crystal lens array with a hexagonal arrangement is investigated experimentally. The uniqueness of this study exists in the fact that using convex-ring electrode provides a smooth and controllable applied potential profile across the aperture to manage the phase profile. We observed considerable differences between flat electrode and convex-ring electrode; in particular the lens focal length is variable in a wider range from 2.5cm to infinity. This study presents several noteworthy characteristics such as low driving voltage; 30 µm cell gap and the lens is electrically switchable between 2D/3D modes. We demonstrate a hexagonal LC-lens array for capturing 3D images by using single sensor using integral imaging.

High directional backlight using an integrated light guide plate.

A high directional backlight system that combined a composite microstructure light guide plate (LGP) with a collimated light source was proposed for eco-displays. The collimated planar light was expanded from a point light source and guided towards the normal direction by utilizing the micro-prism array on LGP. High uniformity of spatial luminous, 91%, with a narrow viewing cone of ± 4° can be achieved without additional optical films. Moreover, compared to the conventional backlight, only 5% of power consumption was needed to keep the same luminance, hence, the optical efficiency increased by a factor of 1.47.

Highly anisotropic metasurface: a polarized beam splitter and hologram.

Two-dimensional metasurface structures have recently been proposed to reduce the challenges of fabrication of traditional plasmonic metamaterials. However, complex designs and sophisticated fabrication procedures are still required. Here, we present a unique one-dimensional (1-D) metasurface based on bilayered metallic nanowire gratings, which behaves as an ideal polarized beam splitter, producing strong negative reflection for transverse-magnetic (TM) light and efficient reflection for transverse-electric (TE) light. The large anisotropy resulting from this TE-metal-like/TM-dielectric-like feature can be explained by the dispersion curve based on the Bloch theory of periodic metal-insulator-metal waveguides. The results indicate that this photon manipulation mechanism is fundamentally different from those previously proposed for 2-D or 3-D metastructures. Based on this new material platform, a novel form of metasurface holography is proposed and demonstrated, in which an image can only be reconstructed by using a TM light beam. By reducing the metamaterial structures to 1-D, our metasurface beam splitter exhibits the qualities of cost-efficient fabrication, robust performance, and high tunability, in addition to its applicability over a wide range of working wavelengths and incident angles. This development paves a foundation for metasurface structure designs towards practical metamaterial applications.

Photovoltaic electrical properties of aqueous grown ZnO antireflective nanostructure on Cu(In,Ga)Se2 thin film solar cells.

A solution-grown subwavelength antireflection coating has been investigated for enhancing the photovoltaic efficiency of thin film solar cells. The 100-nm-height ZnO nanorods coating benefited the photocurrent of Cu(In,Ga)Se2 solar cells from 31.7 to 34.5 mA/cm2 via the decrease of surface light reflectance from 14.5% to 7.0%, contributed by the gradual refractive index profile between air and AZO window layer. The further reduction of surface reflectance to 2.3% in the case of 540-nm-height nanorods, yet, lowered the photocurrent to 29.5 mA/cm2, attributed to the decrease in transmittance. The absorption effect of hydrothermal grown ZnO nanorods was explored to optimize the antireflection function in enhancing photovoltaic performances.

A non-selenization technology by co-sputtering deposition for solar cell applications.

This work presents a novel method to form polycrystalline Cu(In(1-x)Ga(x))Se(2) (CIGS) thin film by co-sputtering of In─Se and Cu─Ga alloy targets without an additional selenization process. An attempt was also made to thoroughly elucidate the surface morphology, crystalline phases, physical properties, and chemical properties of the CIGS films by using material analysis methods. Experimental results indicate that CIGS thin films featured densely packed grains and chalcopyrite phase peaks of (112), (220), (204), (312), and (116). Raman spectroscopy analysis revealed chalcopyrite CIGS phase with Raman shift at 175 cm(-1), while no signal at 258 cm(-1) indicated the exclusion of Cu(2-x)Se phase. Hall effect measurements confirmed the polycrystalline Cu(In,Ga)Se2 thin film to be of p type semiconductor with a film resistivity and mobility of 2.19×10(2) Ω cm and 88 cm(2)/V s, respectively.

Liquid crystal panel for high efficiency barrier type autostereoscopic three-dimensional displays.

An autostereoscopic display with parallax barrier attached onto a liquid crystal panel suffers from the trade-off between brightness and crosstalk. One approach for making improvement by modifying the layout of light blocking components, such as thin film transistor, storage capacitor, and protrusion, in the liquid crystal pixel has been proposed. Ray tracing simulation shows that the aperture of the slanted barrier can be significantly increased, hence increasing efficiency, while keeping the same crosstalk level if those light blocking components can be shifted to the corner of the pixel. A six-view 2.83 in. (7.19 cm) prototype has shown improvement on both brightness and crosstalk compared to its counterpart using a traditional liquid crystal panel, which demonstrates an effective approach for a high-efficiency barrier-type autostereoscopic 3D display with a liquid crystal panel.

Microstructure of a newly developed gamma' strengthened Co-base superalloy.

The microstructure of a newly developed Co-base superalloy with enhanced high-temperature strength has been investigated using transmission electron microscopy (TEM) and three-dimensional atom probe (3DAP) techniques. It mainly consists of a typical gamma/gamma' (FCC/L1(2)) structure and a plate-shaped AB3-type (Ni,Co,Cr)3(Ti,Al) intermetallic compound with hexagonal structure (a approximately 5.1A and c approximately 12.5A). gamma' is formed with a bimodal distribution and fine gamma' has a cuboidal morphology. Cr and Co are enriched in the gamma phase, while Ti, Al and Ni are enriched in the gamma' phase. W and Mo are more or less uniformly distributed in both gamma and gamma'. Chemical composition analysis by 3DAP suggests that the plate-shaped phase has a higher Ti and lower Al content compared to that of gamma' phase, and the concentration of Ti, Co and Ni has a periodic variation along c-axis with a period of 12.5A in the plate-shaped phase.

Micro actuated grating for multi-beam optical pickups.

A stress-induced curved polysilicon actuator with a grating is achieved for the application of recordable optical pickups, which have been realized on a single silicon chip using a two-layer poly-silicon and one-layer silicon nitride micro-machining process. Three diffracted beams with equal intensity in each order from the grating were generated while applying a voltage to the actuator. The switching between the single beam and multiple beams can be applied for writing data and reading data in the disc, respectively.