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A simple layer-stacking technique to generate biomolecular and mechanical gradients in photocrosslinkable hydrogels
摘要： Physicochemical and biological gradients are desirable features for hydrogels to enhance their relevance to biological environments for three-dimensional (3D) cell culture. Therefore, simple and efficient techniques to generate chemical, physical and biological gradients within hydrogels are highly desirable. This work demonstrates a technique to generate biomolecular and mechanical gradients in photocrosslinkable hydrogels by stacking and crosslinking prehydrogel solution in a layer by layer manner. Partial crosslinking of the hydrogel allows mixing of prehydrogel solution with the previous hydrogel layer, which makes a smooth gradient profile, rather than discrete layers. This technique enables the generation of concentration gradients of bovine serum albumin in both gelatin methacryloyl (GelMA) and poly(ethylene glycol) diacrylate hydrogels, as well as mechanical gradients across a hydrogel containing varying gel concentrations. Fluorescence microscopy, mechanical testing, and scanning electron microscopy show that the gradient profiles can be controlled by changing both the volume and concentration of each layer as well as intensity of UV exposure. GelMA hydrogel gradients with different Young’s moduli were successfully used to culture human fibroblasts. The fibroblasts migrated along the gradient axis and showed different morphologies. In general, the proposed technique provides a rapid and simple approach to design and fabricate 3D hydrogel gradients for in vitro biological studies and potentially for in vivo tissue engineering applications.
关键词： 3D cell culture,Gelatin methacryloyl,Photocrosslinkable hydrogel,Poly(ethylene glycol) diacrylate,Gradient
更新于2025-11-21 11:24:58
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Planar Phase Gradient Metasurface Antenna with Low RCS
摘要： A low radar cross section (RCS) planar antenna using phase gradient metasurface is proposed in this paper. The proposed antenna works in the X-band and is fed by a parallel plate waveguide power divider. The designed phase gradient metasurface is coplanar with the feeding structure and couples guided waves in the parallel plate waveguide power divider to radiation waves. According to the generalized reflection law, the proposed metasurface is a frequency scanning antenna and the beam direction can be steered slightly from 16.6° to 13°. The proposed antenna is linearly polarized, and however, the RCS is reduced significantly for arbitrary polarized incident waves. The antenna was simulated, fabricated, and measured. The measurement results confirm well with the simulation results.
关键词： frequency scanning,low profile,Phase gradient metasurface,RCS reduction
更新于2025-09-23 15:23:52
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Wave Propagation of Porous Nanoshells
摘要： This study aims at investigating the wave propagation of porous nanoshells. The Bi-Helmholtz non-local strain gradient theory is employed in conjunction with a higher-order shear deformation shell theory, in order to include the size-dependent effects. The nanoshells are made of a porous functionally graded material (P-FGM), whose properties vary continuously along the thickness direction. A variational approach is here applied to handle the governing equations of the problem, which are solved analytically to compute the wave frequencies and phase velocities as function of the wave numbers. The sensitivity of the wave response is analyzed for a varying porosity volume fraction, material properties, non-local parameters, strain gradient length scales, temperature, humidity, and wave numbers. Based on the results, it is verified that the size-dependence of the response is almost the same to the one of plates, beams and tubes.
关键词： doubly-curved nanoshell,wave propagation,higher-order shear deformation shell theory,porous materials,generalized non-local strain gradient theory
更新于2025-09-23 15:23:52
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Radar cross section reduction metasurfaces based on phase gradient and chessboard structure
摘要： In this article, wideband radar cross section (RCS) reduction metasurface is proposed. The unit of the metasurface is consisted of a noncentral symmetry hexagon patch with 2 semi-circular slots at the symmetric corners. As a result, the unit has an anisotropic response for x- and y-polarized wave. The reflection phase is varied with the radius of slots. The range of phase variation is extended by rotation of the unit with 90°. According to the generalized Snell’s Law, 4 different phase gradient supercells with dual polarization characteristics and different gradient directions are obtained. To improve the RCS reduction, chessboard structure is used. By combining these 2 technological approaches, a wideband, polarization insensitive RCS reduction is designed, which can reflect the electromagnetic wave uniformly. Both numerical and measured results show that it enables to realize a 10 dB RCS reduction in a wideband from 8.5 to 13 GHz.
关键词： chessboard structure,metasurface,phase gradient,RCS reduction,phase variation
更新于2025-09-23 15:23:52
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Fracture behavior of carbon fiber reinforced polymer composites: An optical study of loading rate effects
摘要： Crack initiation and growth in single-edge notched unidirectional T800s/3900-2 CFRP laminates are studied under stress wave and quasi-static loading conditions. An optical technique called reflection-mode Digital Gradient Sensing is also extended to study fracture mechanics of CFRP by using it in conjunction with ultrahigh-speed photography to perform full-field measurement of crack-tip deformations in the pre- and post-crack initiation regimes. DGS is capable of measuring two orthogonal surface slopes in the crack-tip vicinity as angular deflection of light rays. A method for extracting crack-tip parameters - the instantaneous crack speed and stress intensity factor (SIFs) histories - associated with the stationary and propagating cracks using measured surface slopes is presented. The effect of fiber orientation in the range 0°-60° relative to the initial notch and two loading rates are investigated. Nominally mode-I fracture occurs when the fiber orientation is 0° whereas mixed-mode fractures ensue in others. Besides crack initiation occurrence at higher loads as fiber orientation increases, the SIF histories imply strong fiber bridging at low fiber orientations under quasi-static conditions. Furthermore, this CFRP shows significant loading rate dependence during crack growth. Unlike stress wave loading conditions, an increasing crack growth resistance immediately after crack initiation is seen under quasi-static conditions.
关键词： Carbon fiber reinforced plastics,Loading rate effects,Crack growth behavior,Dynamic fracture,Digital Gradient Sensing
更新于2025-09-23 15:23:52
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Performance Analysis of Maximum Power Point Tracking Algorithms Under Varying Irradiation
摘要： Photovoltaic (PV) system is one of the reliable alternative sources of energy and its contribution in energy sector is growing rapidly. The performance of PV system depends upon the solar insolation, which will be varying throughout the day, season and year. The biggest challenge is to obtain the maximum power from PV array at varying insolation levels. The maximum power point tracking (MPPT) controller, in association with tracking algorithm will act as a principal element in driving the PV system at maximum power point (MPP). In this paper, the simulation model has been developed and the results were compared for perturb and observe, incremental conductance, extremum seeking control and fuzzy logic controller based MPPT algorithms at different irradiation levels on a 10.2 kW PV array. The results obtained were analysed in terms of convergence rate and their efficiency to track the MPP.
关键词： perturb and observe,fuzzy logic controller,scalar gradient extremum seeking control,Photovoltaic system,incremental conductance,MPPT algorithms
更新于2025-09-23 15:23:52
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Effects of the microstructure and density profiles on wave propagation across an interface with material properties
摘要： The characterization of the interphase condition between two materials is current in mechanics. In general, its modeling is achieved by considering an interface with only purely elastic properties. In this paper, following previous works, also inertial interface properties are taken into account. For sufficiently low-frequency regime, we investigate two density profiles (affine and quadratic), for the interphase. Moreover, the interface and the interphase are placed between two solids with different characteristics. The first one is non-dispersive, while for the second one three cases are considered: (a) solid without microstructure, i.e., a Cauchy continuum, (b) solid with microstructure characterized by normal dispersion, i.e., a strain gradient continuum, and (c) by anomalous dispersion. The reflection coefficients are plotted for each case. These results are evaluated with respect to a benchmark finite elements simulation of the finite heterogeneous interphase, and the error is discussed. It is shown that the effects of microstructure can be appreciated at higher frequencies and that the proposed model results to be accurate.
关键词： Strain gradient,Reflection coefficient,Interface,Interphase,Density profiles,Wave propagation
更新于2025-09-23 15:23:52
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Stacked Nanoporous Anodic Alumina Gradient-Index Filters with Tunable Multispectral Photonic Stopbands as Sensing Platforms
摘要： This study presents the development and optical engineering of stacked nanoporous anodic alumina gradient-index (NAA-GIFs) filters with tunable multi-spectral photonic stopbands for sensing applications. The structure of these photonic crystal (PC) is formed by stacked layers of NAA produced with sinusoidally modified effective medium. The progressive modification of the sinusoidal period during the anodization process enables the generation and precise tuning of the characteristic photonic stopbands (PSB) (i.e. one per sinusoidal period in the anodization profile) of these PC structures. Four types of NAA-GIFs featuring three distinctive PSBs positioned within the visible spectral region are developed. The sensitivity of the effective medium of these NAA-GIFs is systematically assessed by measuring spectral shifts in the characteristic PSBs upon infiltration of their nanoporous structure with analytical solutions of D-glucose with several concentrations (0.025 – 1 M). This study provides new insights into the intrinsic relationship between the nanoporous architecture of these PCs and their optical properties, generating opportunities to fabricate advanced optical sensing systems for high-throughput and multiplexed detection of analytes in a single sensing platform.
关键词： nanoporous anodic alumina,sensing platforms,stacked,multispectral bands,photonic crystals,gradient index filters
更新于2025-09-23 15:23:52
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Perovskite photocatalyst CsPbBr3-xIx with a bandgap funnel structure for H2 evolution under visible light
摘要： A simple and efficient light-assisted method is employed to prepare powder samples of all-inorganic mixed-perovskite CsPbBr3-xIx from CsPbBr3 by ion exchange in aqueous HBr/KI solution such that the concentration of I in a sample particle decreases on going from the surface to the interior. CsPbBr3-xIx/Pt, namely, CsPbBr3-xIx samples loaded with Pt nanoparticles, shows a high performance for the hydrogen evolution under visible-light irradiation in aqueous HBr solution saturated with CsPbBr3. The H2 evolution rate of the CsPbBr3-xIx/Pt powders (200 mg) is determined to be 224 μmol h-1, under 120 mW cm-2 visible-light (λ ≥ 420 nm) illumination. The CsPbBr3-xIx samples have a high stability, with no apparent decrease in the catalytic activity after 50 h of repeated H2 evolution experiments. The apparent quantum efficiency of CsPbBr3-xIx/Pt is determined to be 2.15% under the irradiation of 450 nm light.
关键词： photocatalysis,hydrogen evolution,bandgap funnel,all-inorganic perovskite,halide gradient
更新于2025-09-23 15:23:52
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Exploring approximate geometries of minimum energy conical intersections by TDDFT calculations
摘要： An approach is proposed to obtain approximate geometries for minimum energy conical intersections between the ground and first excited singlet electronic states (S0/S1-MECIs) using the time-dependent density functional theory (TDDFT). This approach uses the energy shift method to avoid discontinuities on TDDFT potential energy surfaces around conical intersections. It is shown numerically that the approximate S0/S1-MECIs of benzene and naphthalene obtained by this approach qualitatively reproduce the geometries and energies of the S0/S1-MECIs obtained by multireference theories. Moreover, the performance of the present approach when combined with an automated MECI searching method is examined through applications to benzene and naphthalene.
关键词： energy shift method,time dependent density functional theory,gradient projection,single component artificial force induced reaction,conical intersection,global reaction route mapping
更新于2025-09-23 15:23:52