9,185 research outputs found
Function-led design of multifunctional stimuli-responsive superhydrophobic surface based on hierarchical graphene-titania nanocoating
Multifunctional smart superhydrophobic surface with full-spectrum tunable
wettability control is fabricated through the self-assembly of the graphene and
titania nanofilm double-layer coating. Advanced microfluidic manipulative
functions, including directional water transport, adhesion & spreading
controls, droplet storage & transfer, and droplet sensing array, can be readily
realized on this smart surface. An in-depth mechanism study regarding the
underlying secrets of the tunable wettability and the UV-induced
superhydrophilic conversion of anatase titania are also presented
Efficient Thermal Image Segmentation through Integration of Nonlinear Enhancement with Unsupervised Active Contour Model
Thermal images are exploited in many areas of pattern recognition applications. Infrared thermal image segmentation can be used for object detection by extracting regions of abnormal temperatures. However, the lack of texture and color information, low signal-to-noise ratio, and blurring effect of thermal images make segmenting infrared heat patterns a challenging task. Furthermore, many segmentation methods that are used in visible imagery may not be suitable for segmenting thermal imagery mainly due to their dissimilar intensity distributions.
Thus, a new method is proposed to improve the performance of image segmentation in thermal imagery. The proposed scheme efficiently utilizes nonlinear intensity enhancement technique and Unsupervised Active Contour Models (UACM). The nonlinear intensity enhancement improves visual quality by combining dynamic range compression and contrast enhancement, while the UACM incorporates active contour evolutional function and neural networks.
The algorithm is tested on segmenting different objects in thermal images and it is observed that the nonlinear enhancement has significantly improved the segmentation performance
Optical Yagi-Uda nanoantennas
Conventional antennas, which are widely employed to transmit radio and TV
signals, can be used at optical frequencies as long as they are shrunk to
nanometer-size dimensions. Optical nanoantennas made of metallic or
high-permittivity dielectric nanoparticles allow for enhancing and manipulating
light on the scale much smaller than wavelength of light. Based on this
ability, optical nanoantennas offer unique opportunities regarding key
applications such as optical communications, photovoltaics, non-classical light
emission, and sensing. From a multitude of suggested nanoantenna concepts the
Yagi-Uda nanoantenna, an optical analogue of the well-established
radio-frequency Yagi-Uda antenna, stands out by its efficient unidirectional
light emission and enhancement. Following a brief introduction to the emerging
field of optical nanoantennas, here we review recent theoretical and
experimental activities on optical Yagi-Uda nanoantennas, including their
design, fabrication, and applications. We also discuss several extensions of
the conventional Yagi-Uda antenna design for broadband and tunable operation,
for applications in nanophotonic circuits and photovoltaic devices
Sol-Gel Assembly of Metal Nanostructures into Metallic Gel Frameworks and Their Applications
The advent of nanoscience and nanotechnology has sparked many research forefronts in the creation of materials with control over size, shape, composition, and surface properties.1,2 However, for most of the applications, nanoscale materials need to be assembled into functional nanostructures that exhibit useful and controllable physical properties. Therefore, numerous efforts on the assembly of nanoparticles (NPs) using organic ligands, polymers and polyelectrolytes have been reported.3,4 However, the interactions between NPs are mediated by intervening ligands, which are detrimental to charge transport and limit the thermal stability. Hence, developing a new method to produce solid state nanostructures with direct NP linkage has become a significant challenge. To avoid the bridging ligands and improve the conductivity of NP based solid state structures, a novel strategy has been developed in which colloidal NPs undergo condensation to wet “jello-like” hydrogel with direct interfacial linkage. Then hydrogels can be dried supercritically to produce aerogels.5 Resultant nanostructures exhibit low densities, large open interconnected pores, and high internal surface areas and are containing entirely of colloidal metal NPs.6 Since noble metal NPs have been widely used in applications such as catalysts, sensors, and novel electrochemical device components, we herein expanded the sol-gel method to noble metal NPs to produce a new class of metal aerogels.
In the dissertation, the synthesis of hollow Ag hollow NPs, Au/Ag alloy NPs, and Au/Pt/Ag alloy hollow NPs with tunable sizes and physical properties, and their oxidative-assembly into high-surface-area, mesoporous, self-supported gel framework has been achieved. The gelation kinetics have been controlled by tuning the oxidant/thiolate molar ratio that governs the rate of NP condensation, which in turn determines the morphology, optical transparency, surface area, and porosity of the gel frameworks. These low-density mesoporous nano-architectures displaying optical transparency or opacity, enormously surface area, and interconnected meso-to-macro pore structure are promising candidates for catalytic, electrocatalytic, and SERS-based sensing applications. The SERS activity of Au/Ag alloy aerogels has been studied and significant signal enhancement was achieved. The performance of the Au/Pt/Ag aerogel towards methanol oxidation reaction has been studied via cyclic voltammetry and significant electro-catalytic activity was observed
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Lead halide perovskite nanowires stabilized by block copolymers for Langmuir-Blodgett assembly
The rapid development of solar cells based on lead halide perovskites (LHPs) has prompted very active research activities in other closely-related fields. Colloidal nanostructures of such materials display superior optoelectronic properties. Especially, one-dimensional (1D) LHPs nanowires show anisotropic optical properties when they are highly oriented. However, the ionic nature makes them very sensitive to external environment, limiting their large scale practical applications. Here, we introduce an amphiphilic block copolymer, polystyrene-block-poly(4-vinylpyridine) (PS-P4VP), to chemically modify the surface of colloidal CsPbBr3 nanowires. The resulting core-shell nanowires show enhanced photoluminescent emission and good colloidal stability against water. Taking advantage of the stability enhancement, we further applied a modified Langmuir-Blodgett technique to assemble monolayers of highly aligned nanowires, and studied their anisotropic optical properties. [Figure not available: see fulltext.]
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