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Mesoscopic Analysis of Fatigue Damage Development in Asphalt Mixture Based on Modified Burgers Contact Algorithm in Discrete Element Modeling.

This study is aimed at examining the mesoscopic mechanical response and crack development characteristics of asphalt mixtures using the three-dimensional discrete element approach via particle flow code (PFC). The material is considered an assembly of three phases of aggregate, mortar, and voids, for which three types of contact are identified and described using a modified Burgers model allowing for bond failure and crack formation at contact. The laboratory splitting test is conducted to determine the contact parameters and to provide the basis for selecting three different load levels used in the indirect tensile fatigue test and simulation. The reliability of the simulation is verified by comparing the fatigue lives and dissipated energies against those from the test. Under cyclic loading, the internal tensile and compressive force chains vary dynamically as a response to the cyclic loading; both are initially concentrated beneath the top loading strip and then extend downward along the loading line. The compressive chains are oriented roughly vertically and develop an elliptic shape as damage grows, while the tensile chains are mostly horizontal and become denser. An analysis based on the histories of the numbers of different contact types indicates that damage mainly originates from bond failures among the aggregate particles and at the aggregate-mortar interfaces. In terms of location, cracking is initiated below the loading point (consistent with observations from the force chains) and propagates downward and laterally, leading to the macrocrack along the vertical diameter. The findings provide a mesoscopic understanding of the fatigue damage initiation and propagation in asphalt mixture.

Strip-loaded Mach–Zehnder interferometer for absolute refractive index sensing

This paper presents the design, fabrication, and characterization of a Mach–Zehnder interferometer (MZI) on a strip-loaded platform specifically developed for the measurement of refractive index variations in liquids. A novel approach of large opening in the sensing region enhances the sensitivity by using the analyte as the loading strip. This allows surpassing the performances of the conventional perforations and trenched-based MZIs and prevent protecting the reference arm. The implementation of this design resulted in a high confinement factor of approximately 23%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\%$$\\end{document} in the cladding, enabling an effective interaction between the evanescent field and analyte. Ethanol-water solutions with varying concentrations were used as analyte for the characterization of the device. The strip-loaded waveguide was a 200 nm TiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document} thin film on a silicon dioxide wafer and a 1.2 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu $$\\end{document}m wide for 800 nm-thick nLOF resist served as loading strip. The sensing area featured a 10 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu $$\\end{document}m wide open-ing in the loading material with a sensing length of 5 mm. The homogeneous sensitivity was experimentally determined to be 0.128, demonstrating the effectiveness of the proposed design, which enabled a refractive index change monitoring of 10-6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-6}$$\\end{document}.

Hybrid silica and thin-film lithium niobate waveguides and Y-junctions

Silica (SiO2) strip-loaded waveguides and Y-junctions on lithium niobate (LN) thin film were designed, fabricated and experimentally investigated. We first studied the optical confinement factor distribution in strip-loaded waveguides. The Simulations showed that most of the power (>82%) was confined in the LN layer, and the dimensions of the SiO2 loading strip had a relatively small influence on the optical confinement factor distribution. The SiO2 film was deposited with the magnetron sputtering method. The deposited SiO2 layer approached stoichiometric SiO2, and a smooth surface was obtained. A group of waveguides with widths of 2–5 μm were fabricated using lift-off technology. The 2 μm-wide waveguide displayed low propagation losses of 0.2 dB/cm for the quasi-TE (q-TE) mode and 0.8 dB/cm for the quasi-TM (q-TM) mode at the wavelength of 1550 nm. Y-junctions with small sizes were designed and fabricated based on the low-loss waveguides. The transmission could reach 70–80%, and the splitting ratio maintained at a stable level near 1:1 for the Y-junctions S1 and S4. The low-loss strip-loaded waveguides and Y-junctions offer the possibility of combining SiO2 and LN materials for integrated optics. Additional high-performance photonic devices and circuits using this method are expected in the future.

Electro-optical tunable interleaver in hybrid silicon and lithium niobate thin films.

The interleaver was one of the key devices in dense wavelength division multiplexing (DWDM) applications. In this study, an interleaver with an asymmetrical Mach-Zehnder interferometer structure was designed, fabricated, and characterized in hybrid silicon and lithium niobate thin films (Si-LNOI). The interleaver based on Si-LNOI could be fabricated by mature processing technology of Si photonic, and it was capable of the electro-optical (E-O) tuning function by using the E-O effect of LN. In the range of 1530-1620 nm, the interleaver achieved a channel spacing of 55 GHz and an extinction ratio of 12-28 dB. Due to the large refractive index of Si, the Si loading strip waveguide based on Si-LNOI had a compact optical mode area, which allowed a small electrode gap to improve the E-O modulation efficiency of the interleaver. For an E-O interaction length of 1 mm, the E-O modulation efficiency was 26 pm/V. The interleaver will have potential applications in DWDM systems, optical switches, and filters.

Phase modulators in hybrid silicon and lithium niobate thin films

The hybridization of mono-crystalline silicon and lithium niobate thin films (Si-LNOI) can combine the physical properties of Si and the optical properties of LN, and it has emerged as a new material platform for integrated photonics. In this paper, phase modulators in Si-LNOI were demonstrated. First, the phase modulator was designed. According to the simulation, the Si loading strip waveguide had a small mode area due to the large refractive index of Si. This allowed a small electrode gap that resulted in enhancement of the overlap of the optical field and the electrostatic field, and the VπL of the phase modulator could be as small as 3.3 V·cm. Second, phase modulators with a Si loading strip waveguide with a top width of 0.5 μm were fabricated by plasma etching, and the VπL of the phase modulator was measured to be 4.74 V·cm. This study provides useful information for the devices in the Si-LNOI.

Size effect at aggregate level in microCT scans and DEM simulation – Splitting tensile test of concrete

The paper describes an experimental and numerical study of size effect on concrete cylindrical specimens in splitting tensile test. Own experimental campaign was performed on specimens with 5 various diameters from D = 74, 105, 150, 192 and 250 mm with hardboard loading strips (distributed load according to standard methods) scaled proportionally to the specimen diameter. The crack opening-control system was applied to obtain the post-peak behaviour of all tested specimens including catastrophic behaviour (snap-back). The tested specimens at a certain point were unloaded and scanned with novel high-resolution micro tomography to analyse the macro cracks and phenomena like aggregate breakage, crack branching etc. at the aggregate level. Based on realistic mesostructure the discrete element method (DEM) 2D model of 3 specimens with diameters of D = 74, 150 and 250 mm were constructed and tested. The fracture was analysed at macro and micro-level in DEM and directly compared with microCT scans. DEM simulations revealed additional information related to the loss of material strength and ductility with increasing specimen size (size effect). The simulation and experimental results were in good agreement.

Strip-loaded horizontal slot waveguide for routing microdisk laser emission

A strip-loaded horizontal slot waveguide is used for routing the emission of a microdisk laser. The active region of the laser contains InAs/InGaAs/GaAs quantum dots operating in CW mode under optical pumping. Although the quantum dots emit in a broad range, the laser emission is single mode with λ = 1290 nm . Atomic layer deposition is used for the fabrication of the TiO 2 / SiO 2 / TiO 2 slot waveguide covering the 10-µm-diameter disk. The horizontal slot waveguide covers the microdisk and traps the emission in the fundamental TM mode of the three-stack layer. Once light is localized inside this planar waveguide, a loading strip creates an effective index difference, which is sufficient to confine the mode laterally and leads to the guiding of the lasing emission. An analytical model for the five-layer horizontal planar slot waveguide was developed in order to optimize the slot waveguide according to the operation wavelength of the microlaser and the different materials involved. Scanning near-field optical microscopy is used to observe the propagation of light within the waveguide and confirm the mode coupling into it and therefore the guiding along the loading strip.

Modelling the flow of asphalt under simulated compaction using discrete element

The flow differences between the particles of asphalt mixtures compacted in the laboratory and in the field have been identified as one of the reasons for the discrepancies between laboratory and field results. In previous studies, the authors developed a simplified test method, the so-called compaction flow test (CFT), for roughly simulating the flow of particles in asphalt mixtures under compacting loads in laboratory. The CFT was used in different studies to examine its capability of revealing the differences between the flow behavior of different asphalt mixtures under various loading modes. The promising results encouraged further development of the CFT by investigating the possible impacts of simplifications and boundary conditions on the results of this test. For this reason, discrete element method (DEM) was utilized to investigate possible impacts of the mold size, geometry of the loading strip as well as the loading rate on the results of the CFT. The results of the simulation indicate that in case of wearing course layers with nominal maximum aggregate size of 11 mm, the length of the CFT mold can be increased from 150 mm to 200–250 mm for reducing flow disturbances from the mold walls. However, since the majority of the flow of asphalt mixture particles is expected to take place within the first 100–150 mm length of the mold, reasonable results can still be obtained even without changing the size of the CFT mold. Moreover, comparing results with different loading strip geometries and loading rates indicates that the current CFT setup still appears to provide consistent results.

Strip-loaded nano-photonics on horizontal slot waveguide

BackgroundA strip-loaded slot waveguide is a waveguide platform allowing a large amount of degrees of freedom in terms of fabrication. Contrary to other waveguide types where the guiding layer has to be patterned, only the shape of the top layer, usually a polymer, dictates the response of this platform.MethodsWe use the Finite Difference Time Domain method to study the field distribution and the modal behavior of light inside such a waveguide when the loading strip is patterned.ResultsWe present an overview of several photonic-crystal-based structures on a strip-loaded slot waveguide platform. This theoretical study shows how the fundamental mode confined in the horizontal slab slot waveguide interacts with the dielectric loading structures. By investigating the field confinement, one determines the importance of the longitudinal shape over the lateral shape of the loading structure. Through the examples of sidewall corrugation, row of cylindrical or elliptical holes, and random shapes, we show how such a platform can help integration of complex functions in waveguides.ConclusionsAlthough the spectral features depend strongly on the period and fill factor of the Bragg gratings studied in our case, the material distribution plays a key-role in the mode behavior. This impacts directly on the applications of such a platform for further modulators and sensors, for instance.

Establishing a resilient modulus test protocol for miniature cylindrical asphalt mix specimens

The resilient modulus is a very important parameter to be identified and used in pavement design. The indirect tensile test is the most common repeated load test to measure the resilient modulus of asphalt mixtures and the easiest method to test laboratory compacted specimens and field core specimens. The resilient moduli of asphalt mixtures are measured using the indirect tensile procedure (ASTM D4123). A metal loading strip with a concave surface with the radius of the test specimen is required to apply load to the specimen. Typically, specimens are either a nominal 100mm or 150mm in diameter with a minimum thickness over diameter ratio of 0.4. However, typical 100mm diameter core samples with 40mm to 50mm thickness taken from the site most often do not fulfil the minimum ratio of 0.4 after the samples are trimmed for testing. As such, a new procedure was developed to test specimens smaller than 100mm in diameter. This expected to be very useful and minimize the volume requirement from the field. This novel protocol for resilient modulus test using miniature specimens of 37.5mm and 56.3mm in diameter has great potential for practical relevance for the industry.

Dynamic operation and modelling of amine-based CO2 capture at pilot scale

This study combines pilot plant experiments and dynamic modelling to gain insight into the interaction between key process parameters in producing the dynamic response of an amine-based CO2 capture process. Three dynamic scenarios from the UKCCSRC PACT pilot plant are presented: (i) partial load stripping, (ii) capture plant ramping, and (iii) reboiler decoupling. These scenarios are representative of realistic flexible operation of non-baseload CCS power stations. Experimental plant data was used to validate a dynamic model developed in gCCS. In the capture plant ramping scenario, increased liquid-to-gas (L/G) ratio resulted in higher CO2 capture rate. The partial load stripping scenario demonstrated that the hot water flow directly affects reboiler temperature, which in turn, has an impact on the solvent lean loading and CO2 capture rate. The reboiler decoupling scenario demonstrates a similar relationship. Turning off the heat supply to the reboiler leads to a gradual decline in reboiler temperature, which increases solvent lean loading and reduces CO2 capture rate. The absorber column temperature profile is influenced by the degree of CO2 capture. For scenarios that result in lower solvent lean loading, the absorber temperature profile shifts to higher temperature (due to the higher CO2 capture rate).

Liquid-liquid extraction and recovery of Cerium(IV) and Phosphorus from sulfuric acid solution using Cyanex 923

The work addresses the extraction and separation of cerium(IV) (Ce(IV)) and phosphorus (P) from a H2SO4 solution using Cyanex 923 diluted in n-heptane. The effects of H2SO4 concentration, extractant concentration and P concentration on the extraction have been investigated. The thermodynamic parameters have been determined, showing that the extraction is exothermic. The saturation load capacity and stripping efficiency are discussed in the report. The results of FTIR and NMR show that Ce(IV) and P can form complex in the sulfuric acid media and then are extracted into organic phase by the interaction of Ce(IV) in complex with PO of Cyanex 923. The extraction process was studied. CePO4 powder was prepared by reductive stripping of the loaded organic phase with H2O2. The powder was characterized by XRD and DSL. Because of the high saturation load capacity and stripping efficiency, Cyanex 923 was validated to be a promising extractant for Ce(IV) and P from the H2SO4 solution, providing a potential application for the recovery of Ce(IV) and P from Bayan Obo mixed RE ores.

Microstrip Leaky-Wave Antennas With Nonuniform Periodical Loading of Shorting Pins for Enhanced Frequency Sensitivity

This paper investigates on an effective approach to enhance frequency sensitivity of the classic wideband EH1-mode microstrip leaky-wave antenna (MLWA). Nonuniform loadings of shorting pins are installed into the traditional EH1-mode microstrip line, which provide a unique discontinuity affecting the mutual intersection of the passband and stopband, thus generating a newly created stopband within the continuous EH1-mode fast-wave region. After broadening the stopband, the slope of normalized phase constant is remarkably raised up and the original wide bandwidth of the operating region is effectively reduced, resulting in a dramatically enhanced frequency sensitivity. An equivalent-circuit model of the proposed EH1-mode MLWA with nonuniform loading is built up at first, then its nonuniform loading discontinuity effect on dispersion transformation between passband and stopband is further explicated. Moreover, full-wave numerical extraction is also conducted to accurately demonstrate the modified phase constant under varied lateral pins’ loading positions and strip widths. After thorough discussion, one set of optimized parameters are selected into antenna design. Compared with the conventional counterpart, the proposed EH1-mode MLWA with nonuniform loading of shorting pins notably increases the frequency sensitivity from 0.038°/MHz to 0.135°/MHz.

Experimental and numerical investigations of concrete behaviour at meso-level during quasi-static splitting tension

The paper describes experimental and numerical results of quasi-static splitting tensile tests on concrete specimens at meso-scale level. The experiments were carried out on cylindrical specimens with the diameter of 0.15 m. The loading strip was made of plywood or steel. Fracture in concrete was detected at the aggregate level by means of three non-destructive methods: 3D X-ray micro-computed tomography, 2D scanning electron microscope and manual 2D digital microscope. The discrete element method was used to directly simulate experiments at the meso-scale. Concrete was modelled as a random heterogeneous 4-phase material composed of aggregate particles, cement matrix, interfacial transitional zones and macro-voids based on micro-tomographic images. Two-dimensional calculations with real concrete microstructure were carried out. The effect of the different loading/supporting strip type on the stress-strain curve and fracture process was studied. This effect proved to be significant. A satisfactory agreement between numerical and experimental results was achieved. The evolution of contact normal forces, coordination number, broken contacts, grain rotations and crack displacements was also investigated. In addition, each energy component was calculated and analyzed at a different stress-displacement stage.

Amorphous silicon-lithium niobate thin film strip-loaded waveguides

The heterogeneous integration of an amorphous silicon (a-Si) film with a lithium niobate (LN) thin film combines both the mature micro-processing technology of Si and the excellent optical properties of LN. An a-Si thin film was deposited on an LN thin film, and strip-loaded waveguides were designed, fabricated, and characterized. A full-vectorial finite difference method was used to explore the single-mode conditions and appropriate dimensions for the strip-loaded waveguides. The waveguide mode size could be as small as 0.36 μm2. By adjusting the thickness and width of the a-Si loading strip, the distribution of light power could be mainly confined in the LN layer. The maximal light power that could be confined in LN was 91%, which was obtained at an a-Si thickness of 65 nm. A set of waveguides with widths of 2‒7 μm were prepared by inductively coupled plasma (ICP) etching of the a-Si thin film. Following annealing at 300°C in air for 1 hour, light transmission was observed in the waveguide. The 2-μm-wide waveguide showed propagation losses of 20 dB/cm for the quasi-TM (q-TM) mode and 42 dB/cm for the quasi-TE (q-TE) mode at 1550 nm. The root-mean-square (RMS) surface roughness of the a-Si thin film before and after annealing was 1.04 and 0.35 nm, respectively. High-resolution transmission electron microscopy (HRTEM) was performed to investigate the interface morphologies. A well-defined interface was clearly observed, and the structure of the a-Si thin film was proved to be amorphous.

Strip-loaded waveguide on titanium dioxide thin films by nanoimprint replication.

We present a convenient, low-cost, and mass-production-compatible technique for the fabrication of strip-loaded waveguides. The technique is based on the atomic layer deposition of a slab waveguide, nanoimprinting of a strip, and integration of two structures by lamination. The guiding layer is chosen to be a 200nm thick titanium dioxide film. The waveguide characteristics are determined by the use of ring resonators. The technique is demonstrated for titanium dioxide thin films, but it is applicable to any other material that meets the refractive index difference condition between the loading strip and the slab waveguide.

Influence of the Width of the Loading Strip in the Brazilian Tensile Test of Concrete and Other Brittle Materials

AbstractDifficulties presented by the direct tensile test of nonhomogeneous, brittle materials were circumvented by the proposal of an indirect tensile test for concrete, known in the literature as the Brazilian test, which found applications in the technology of concrete, rocks, ceramics and other materials. Relationships between the predictions of the Brazilian test and the results of both the direct tensile test and the unconfined compression test have been proposed on the basis of experimental evidence. On the other hand, developments in numerical fracture analysis allowed for the examination of the fracture process in the test, including the consideration of scale and rate effects. The discrete element method was used to determine the nonlinear response of brittle solids and to predict the response of simulated concrete samples subjected to indirect tensile tests. This paper extends this approach to more precisely quantify the role of factors such as the width and stiffness of the strips inserted bet...

The Sustainable and Efficient Ionic Liquid-Type Saponification Strategy for Rare Earth Separation Processing

For the development of sustainable and efficient separation technology for rare earth elements (REEs), the ionic liquid-type saponification strategy is first put forward in this paper. The extraction mechanism of [trihexyl(tetradecyl)phosphonium][sec-octylphenoxy acetate] ([P6,6,6,14][SOPAA]) prepared by ionic liquid-type saponification for Y(III) was indicated to be ion association. The mechanism contributes to avoiding the numerous saponification procedures and resulting saponification wastewater in the REE separation industry. Load capacity and stripping properties of [P6,6,6,14][SOPAA] reveal advantages over its precursory sec-octylphenoxy acetic acid (HSOPAA). Extractability and selectivity of [P6,6,6,14][SOPAA] for Y(III) are pronouncedly better than those of HSOPAA. Multistage extraction using functional ionic liquid as extractant for different REE separations is developed. After five stages of extraction sections and four stages of scrubbing sections, Lu(III) was successfully separated from Y(III)...

Miniaturised design of coplanar waveguide‐fed broadband circularly polarised slot antenna

A novel miniaturised design of broadband circularly polarised (CP) antenna using a coplanar waveguide feed is presented. To realise CP characteristic, a pair of inverted-L strips around two opposite corners of the slot is protruded. By properly folding the modified ground plane, the 3-dB axial-ratio (AR) band is shifted to around a lower-frequency location, whereas the input impedance band is shifted downwards through the Y-shaped loading strip. The overall size of the antenna is about 0.34 λ 0 × 0.34 λ 0 × 0.009 λ 0 at 1.7 GHz. Measured results show that the proposed design can deliver 3-dB AR bandwidth of 36.8% (1.55–2.25 GHz) and 10 dB impedance bandwidth of 63.2% (1.17–2.25 GHz).

Tunable millimeter-wave phase shifter based on dielectric elastomer actuation

A very low-loss tunable millimeter-wave phase shifter driven by dielectric elastomer actuators (DEAs) is presented. The device consists of a fixed coplanar waveguide (CPW) and two metallic loading strips suspended on an elastomer membrane. The horizontal offset between the CPW and the strips is dynamically controlled by integrated DEAs. The variable interaction between the CPW and the loading strips results in a change in the effective permittivity, thereby providing analog-controlled true-time-delay. The design, fabrication, and measurements of this phase shifter based on DEAs are presented, demonstrating state-of-the-art phase shift to loss performance, achieving 235°/dB at 35 GHz.