Thin Grid Research Articles

What Goes Around Comes Around: Covering Tours and Cycle Covers with Turn Costs

We investigate several geometric problems of finding tours and cycle covers with minimum turn cost, which have been studied in the past, with complexity, approximation results, and open problems dating back to work by Arkin et al. in 2001. Many new practical applications have spawned variants: For full coverage, all points have to be covered, for subset coverage, specific points have to be covered, and for penalty coverage, points may be left uncovered by incurring a penalty. We show that finding a minimum-turn (full) cycle cover is NP-hard even in 2-dimensional grid graphs, solving the long-standing open Problem 53 in The Open Problems Project edited by Demaine, Mitchell and O’Rourke. We also prove NP-hardness of finding a subset cycle cover of minimum turn cost in thin grid graphs, for which Arkin et al. gave a polynomial-time algorithm for full coverage; this shows that their boundary techniques cannot be applied to compute exact solutions for subset and penalty variants. We also provide a number of positive results. In particular, we establish the first constant-factor approximation algorithms for all considered subset and penalty problem variants for grid-based instances, based on LP/IP techniques. These geometric versions allow many possible edge directions (and thus, turn angles, such as in hexagonal grids or higher-dimensional variants); our approximation factors improve the combinatorial ones of Arkin et al.

Enhancement of the Robustness on Advancing Layer Method with Trimmed Hexahedral Volume Mesh for the Generation of the Boundary Layer Grids

When performing simulations using computational fluid dynamics, the grid systems in the viscous boundary layer regions are important because the velocity and pressure change very rapidly in these regions. Especially for the turbulent flows, thin grids should be arranged densely in the direction perpendicular to the wall. In this study, the advancing layer method, which has been applied mostly to tetrahedral meshes, is applied to trimmed hexahedral meshes. To generate boundary layer meshes with non-intersecting grid lines near the wall boundaries having concave corners and narrow gaps, the directional vectors of grid lines and faces are smoothed, and the displacement vector fields calculated using the Laplace equation were utilized. Firstly, the details on the newly developed methods are introduced showing simple two-dimensional cases as examples. After applying the methods for a complex three-dimensional geometry to check its applicability and investigating the generated grid systems, the numerical simulations of propeller open water test for INSEAN E779A marine propeller were carried out by simpleFoam, one of the standard solvers of OpenFOAM. The computational results showed good agreement with the experimental results. Therefore, in conclusion, the developed advancing layer method is an appropriate method for generating boundary layer grids of a trimmed hexahedral mesh.

Technique for Producing Metal Oxide Thin-Film Transistors at Low Temperatures

This research presents a novel method for manufacturing metal oxide thin-film transistors (TFTs) at low temperatures. The method involves coupling a metal-oxide film semiconductor to a thin film grid dielectric layer. By carefully controlling the combustion of a fuel-oxidant mixture, the desired metal-oxide film semiconductor is formed at temperatures below 350°C. This approach offers a cost-effective and scalable solution for producing high-performance TFTs on flexible plastic substrates.

Methacrylated Silk Fibroin Additive Manufacturing of Shape Memory Constructs with Possible Application in Bone Regeneration.

Methacrylated silk (Sil-MA) is a chemically modified silk fibroin specifically designed to be crosslinkable under UV light, which makes this material applicable in additive manufacturing techniques and allows the prototyping and development of patient-specific 2D or 3D constructs. In this study, we produced a thin grid structure based on crosslinked Sil-MA that can be withdrawn and ejected and that can recover its shape after rehydration. A complete chemical and physical characterization of Sil-MA was first conducted. Additionally, we tested Sil-MA biocompatibility according to the International Standard Organization protocols (ISO 10993) ensuring the possibility of using it in future trials. Sil-MA was also tested to verify its ability to support osteogenesis. Overall, Sil-MA was shown to be biocompatible and osteoconductive. Finally, two different additive manufacturing technologies, a Digital Light Processing (DLP) UV projector and a pneumatic extrusion technique, were used to develop a Sil-MA grid construct. A proof-of-concept of its shape-memory property was provided. Together, our data support the hypothesis that Sil-MA grid constructs can be injectable and applicable in bone regeneration applications.

Thermally switchable, bifunctional, scalable, mid-infrared metasurfaces with VO2 grids capable of versatile polarization manipulation and asymmetric transmission

We conceptualized three-array scalable bifunctional metasurfaces comprising only three thin strip grids and numerically determined their characteristics in the mid-infrared spectral regime for switchable operation scenarios involving polarization manipulation and related diodelike asymmetric transmission (AT) as one of two functionalities. A few or all of the grids were taken to be made of VO2, a bifunctionality-enabling phase-change material; there are no layers and/or meta-atoms comprising simultaneously both metal and VO2. For each proposed metasurface, two effective structures and, therefore, two different functionalities exist, corresponding to the metallic and insulating phases of VO2. The achieved scenarios of functionality switching significantly depend on the way in which VO2 is incorporated into the metasurface. Switchable bands of polarization manipulation are up to 40 THz wide. The AT band can be modulated when Fabry–Perot (anti-) resonances come into play. Besides, transmission regimes with the cross-polarized component insensitive to VO2 phase change are possible, as well as the ones with all co- and cross-polarized components having the same magnitude for both linear polarizations of the incident wave.

Al2O3-Modified Polymer-Derived Ceramic SiCN High-Temperature Anti-Oxidative Composite Coating Fabricated by Direct Writing.

A reliable protective layer is one of the main challenges in preventing oxidation of thin film sensors to achieve accurate, effective, and stable readings at high temperatures. In this work, an Al2O3-modified polymer-derived ceramic SiCN composite coating fabricated by a direct-writing technique is utilized as a protective layer for thin film sensors. The microstructure evolution of the Al2O3/SiCN films is examined herein. The protective layer exhibits excellent oxidation resistance and thermal stability at high temperatures up to 1000 °C, which contributes to improving the stability and lifetime of thin film sensors in extreme environments. The TiB2/SiCN thin film resistive grid with the Al2O3/SiCN composite film as a protective layer is fabricated and tested. The results indicate that the coating can protect the TiB2/SiCN thin film resistive grid at high temperatures up to 1000 °C, which is about 200 °C higher than that of the TiB2/SiCN thin film resistive grid without a protective layer. The resistance change rates of the TiB2/SiCN thin film resistive grid with a protective layer are 0.5%/h at 900 °C and 10.7%/h at 1000 °C.

Analysis on heat transfer characteristics of integrated circuit silicon chip package based on finite element model

The heating problem of components in integrated circuits has become an important factor affecting the service life and reliability of chips and the whole circuit. In recent years, the study of thermal effects in circuit design and packaging process has become an important topic. In this article, we use comsol software model for integrated circuits, close to the surface of the voltage regulator on simulation circuit boards silicon chips and heat condition of components, each part drawing three dimensional temperature distribution, by changing the voltage regulator for heating power, analysis of the voltage regulator in a certain position in different heating situations on the circuit chip as the core of the influence of the temperature of the parts, Finally, the safe operating range of integrated circuit is obtained without affecting the life of each device. In the simulation process, the thermal thin approximation and grid processing are used, and the temperature distribution map obtained is smooth and continuous, and the circuit structure is fully simulated, which can provide guidance and suggestions for real IC packaging.

A horizontally explicit, vertically implicit (HEVI) discontinuous Galerkin scheme for the 2-dimensional Euler and Navier-Stokes equations using terrain-following coordinates

A solver for the Euler equations with optional diffusion based on the Discontinuous Galerkin (DG) method is presented. To be usable for simulation problems in the atmosphere from the global scale down to the meso-scale, the horizontally explicit, vertically implicit (HEVI) approach is applied to the DG discretization, to avoid tiny time-steps by thin grid cells. To consider orography in the correct approximation order, terrain-following coordinates are used, and to nevertheless keep the local conservation properties of DG, the equations are formulated in the strong conservation form. IMEX-Runge-Kutta time integration enables at least third order approximation in time. In a similar manner, diffusion both as a physical process (for turbulence parameterization) and as a physically motivated stabilization mechanism is treated by the Bassi, Rebay (1997) approach in terrain-following coordinates and in a conserving manner, too. Several test cases relevant for the atmosphere demonstrate the validity of the approach. Although most of the presented theory is applicable both in two and three dimensions (2D and 3D), these test cases are purely 2D. They show, in particular, that the proposed scheme seems to tolerate very steep terrain.

Experimental performance analysis of the concentrated crystalline silicon solar cell——slicing cell

Concentrated photovoltaic (CPV) is raised because of the high cost of solar cells. However, the commercial solar cell is designed with 1 sun. The electrical power will not have the consistent ratio with the increase of concentration ratio. This paper proposes the slicing solar cell to connect commercial cell and CPV. And the experimental research of slicing cells with variable-controlling approach is carried out with different concentration ratio. The results show that slicing design can reduce the output current and power loss caused by series resistance, and remove the upper limit of output current caused by thin grid line. The slicing cell is more suitable for concentrated light condition than normal cell. The power difference between the slicing cell and the normal cell can reach 40 W with 4 suns. Slicing crystalline silicon solar cells have great potential in concentrated photovoltaics.

Improvement of spatial resolution by tilt correction in near-field scanning microwave microscopy

The limitation of mechanical manufacturing will result in a small tilt angle of the sample stage in the horizontal direction, which decreases the spatial resolution of imaging in near-field scanning microwave microscopy (NSMM). In this paper, we focus on the tilt correction and improve the spatial resolution of the NSMM image. The results of electromagnetic simulation and line scan measurement demonstrate the critical parameters affecting the sensitivity of NSMM, such as the length of the probe extending out of the cavity, the tip–sample distance, and the tip apex size. The tilt images can rotate successfully to the horizontal plane with the tilt correction methods, and the local average and re-interpolation are applied to denoise the images. Experimental NSMM images of copper thin film grid, coin texture, lithography mask, and leaf vein are obtained. The images before and after correction verify the improvement of the spatial resolution with all the above methods.

A unified scatter rejection and correction method for cone beam computed tomography.

Scattered radiation is a major cause of image quality degradation in flat panel detector-based cone beam CT (CBCT). While recently introduced 2D antiscatter grids reject the majority of scatter fluence, the small percentage of scatter fluence still transmitted to the detector remains a major challenge for implementation of quantitative imaging techniques such as dual energy imaging in CBCT. Additionally, this residual scatter is also a major source of grid-induced artifacts, which impedes implementation of 2D grids in CBCT. We therefore present a new method to achieve both robust scatter rejection and residual scatter correction using a 2D antiscatter grid; in doing so, we expand the role of 2D grids from mere scatter rejection devices to scatter measurement devices. In our method, the radiopaque septa of the 2D grid emulate a micro array of beam-stops placed on the detector which introduce spatially periodic septal shadows. By selecting sufficiently thin grid septa, the primary intensity can be reduced while preserving the uniformity of scatter intensity. This enables us to correlate the modulated pixel signal intensity in septal shadows with local scatter intensity. Our method then exploits this correlation to measure and remove residual scatter intensity from projections. No assumptions are made about the object being imaged. We refer to this as Grid-based Scatter Sampling (GSS). In this work, we evaluate the principle of signal modulation with grid septa, the accuracy of scatter estimates, and the effect of the GSS method on image quality using simulations and measurements. We also implement the GSS method experimentally using a 2D grid prototype. Our results demonstrate that the GSS method increased CT number accuracy and reduced image artifacts associated with scatter. With 2D grid and residual scatter correction, HU nonuniformity was reduced from 65HU to 30HU in pelvis sized phantoms, and HU variations due to change in phantom size were reduced from 59HU to 20HU, when compared to use of only a 2D grid. With residual scatter correction via GSS method, grid-induced ring artifacts were suppressed, leading to a 41% reduction in noise. The shape of the modulation transfer function (MTF) was preserved before and after suppression of ring artifacts. Our grid-based scatter sampling method enables utilization of a 2D grid as a scatter measurement and correction device. This method significantly improves quantitative accuracy in CBCT, further reducing the image quality gap between CBCT and multi-detector CT. By correcting residual scatter with the proposed method, grid-induced line artifacts in projections and associated ring artifacts in CBCT images were also suppressed with no compromise of spatial resolution.

A retrofitting technique using steel grids for existing masonry panels: a numerical and analytical study

The current research focuses on a numerical and analytical study aimed at investigating the efficiency of a steel-based reinforcement system suitable for existing masonry walls. The application of such a retrofitting technique, which consists of glued thin steel grids applied on both faces of a masonry panel, is reversible, cheap and easy to be executed and appears to be suitable especially for buildings with concrete slab or inter-stories beams to which the steel elements could be anchored. The study is based on a reference experimental test carried out at the “Politehnica” University of Timisoara (Romania), within the European FP6 project PROHITECH. The reference test provided the application of a constant vertical compression and cyclic horizontal displacements to an unreinforced brick-cement mortar wall in full-scale (1500 × 1500 × 250 mm), to which was conferred a double-fixed constraint condition. Based on the experimental evidences, a reference numerical model has been implemented in ABAQUS, by adopting a plastic-damage material and a macro-element approach for the masonry modelling. Hence, in order to determine a design criterion of the studied system, a comparison with the analytical formulations available in the current Italian and European codes for the unreinforced configuration is presented in this study. Then, a wide parametric study on the investigated retrofitting technique has been carried out by varying thickness and spacing of steel grid elements, as well as the geometrical ratio of the panel (height/length). On the basis of the numerical results, a capacity formulation has been proposed, which takes into account the steel distribution in the masonry panel. The obtained outcomes revealed that the strength increase achievable by adopting the studied reinforcement system could be compared to the efficiency of a reinforced masonry wall of new construction and it is strongly influenced by the geometrical ratio of the wall, as well as the steel distribution.

New electrodes for producing nanostructured coatings on aluminum parts using electrospark dopin

It is shown that a new type of electrode is obtained during the process of electrospark doping of the aluminum alloy surfaces, the microstructure of which is a mechanical mixture consisting of grains of high-melting component surrounded by a thin grid of low-melting component, which makes it possible to obtain micro- and nanowires made of low-melting component in the coating and leads to a significant improvement of the wear resistance of the coating. If the specified proportions of the components of the electrode are changed, micro- and nanowires will not be formed in the coating.

The effect of annealing process on the performance of strain nickel–chromium thin film sensor

In order to reduce the resistance value of the sputtering thin film resistor grid and improve the adhesion of the film, a thin film sensor with the NiCr film as a sensitive layer on a 304 stainless steel substrate is annealed in the N2 environment. During the experiment, it is found that the different annealing temperatures (300 °C, 350 °C, 400 °C, 450 °C, and 500 °C) can effectively reduce the resistance value of the thin film resistor grid; the decrease is the largest at 450 °C, and the resistance value change is 1.77 kΩ. The small resistance value enables the thin film sensor to detect smaller strain and has higher measurement accuracy. The thin film has the strongest adhesion on the substrate at 350 °C and 30 min, which is about 37.5% higher than that of the sputtering state. The increase in adhesion makes the thin film less likely to crack and fall off prematurely, which can expand the measuring force range. In addition, the atomic force microscopy results demonstrate that the thin film annealed at a higher annealing temperature has higher surface roughness, which may be caused by the phenomenon of original grain clusters after annealing. In addition, the temperature coefficient of resistance value and strain sensitivity coefficient (kn) increase with the increase in the annealing temperature, with kn increasing only slightly.

Field Proximal Soil Sensor Fusion for Improving High-Resolution Soil Property Maps

Mapping soil properties, using geostatistical methods in support of precision agriculture and related activities, requires a large number of samples. To reduce soil sampling and measurement time and cost, a combination of field proximal soil sensors was used to predict and map laboratory-measured soil properties in a 3.4-ha pasture field in southeastern Brazil. Sensor soil properties were measured in situ on a 10 × 10-m dense grid (377 samples) using apparent electrical conductivity meters, apparent magnetic susceptibility meter, gamma-ray spectrometer, water content reflectometer, cone penetrometer, and portable X-ray fluorescence spectrometer (pXRF). Soil samples were collected on a 20 × 20-m thin grid (105 samples) and analyzed in the laboratory for organic C, sum of bases, cation exchange capacity, clay content, soil volumetric moisture, and bulk density. Another 25 samples collected throughout the area were also analyzed for the same soil properties and used for independent validation of models and maps. To test whether the combination of sensors enhances soil property predictions, stepwise multiple linear regression (MLR) models of the laboratory soil properties were derived using individual sensor covariate data versus combined sensor data—except for the pXRF data, which were evaluated separately. Then, to test whether a denser grid sample boosted by sensor-based soil property predictions enhances soil property maps, ordinary kriging of the laboratory-measured soil properties from the thin grid was compared to ordinary kriging of the sensor-based predictions from the dense grid, and ordinary cokriging of the laboratory properties aided by sensor covariate data. The combination of multiple soil sensors improved the MLR predictions for all soil properties relative to single sensors. The pXRF data produced the best MLR predictions for organic C content, clay content, and bulk density, standing out as the best single sensor for soil property prediction, whereas the other sensors combined outperformed the pXRF sensor for the sum of bases, cation exchange capacity, and soil volumetric moisture, based on independent validation. Ordinary kriging of sensor-based predictions outperformed the other interpolation approaches for all soil properties, except organic C content, based on validation results. Thus, combining soil sensors, and using sensor-based soil property predictions to increase the sample size and spatial coverage, leads to more detailed and accurate soil property maps.

Challenges of Increased Resolution for the Local Ensemble Tangent Linear Model

AbstractAn ensemble-based linearized forecast model has been developed for data assimilation applications for numerical weather prediction. Previous studies applied this local ensemble tangent linear model (LETLM) to various models, from simple one-dimensional models to a low-resolution (~2.5°) version of the Navy Global Environmental Model (NAVGEM) atmospheric forecast model. This paper applies the LETLM to NAVGEM at higher resolution (~1°), which required overcoming challenges including 1) balancing the computational stencil size with the ensemble size, and 2) propagating fast-moving gravity modes in the upper atmosphere. The first challenge is addressed by introducing a modified local influence volume, introducing computations on a thin grid, and using smaller time steps. The second challenge is addressed by applying nonlinear normal mode initialization, which damps spurious fast-moving modes and improves the LETLM errors above ~100 hPa. Compared to a semi-Lagrangian tangent linear model (TLM), the LETLM has superior skill in the lower troposphere (below 700 hPa), which is attributed to better representation of moist physics in the LETLM. The LETLM skill slightly lags in the upper troposphere and stratosphere (700–2 hPa), which is attributed to nonlocal aspects of the TLM including spectral operators converting from winds to vorticity and divergence. Several ways forward are suggested, including integrating the LETLM in a hybrid 4D variational solver for a realistic atmosphere, combining a physics LETLM with a conventional TLM for the dynamics, and separating the LETLM into a sequence of local and nonlocal operators.

Selective multi-nanosoldering for fabrication of advanced solution-processed micro/nanoscale metal grid structures

Solution-processed metal grid transparent conductors with low sheet resistance, high optical transmittance and good mechanical flexibility have great potential for use in flexible optoelectronic devices. However, there are still remaining challenges to improve optoelectrical properties and electromechanical stability of the metallic structures due to random loose packings of nanoparticles and the existence of many pores. Here we introduce a selective multi-nanosoldering method to generate robust metallic layers on the thin metal grid structures (< a thickness of 200 nm), which are generated via self-pining assisted direct inking of silver ions. The selective multi-nanosoldering leads to lowering the sheet resistance of the metal grid transparent conductors, while keeping the optical transmittance constant. Also, it reinforces the electromechanical stability of flexible metal grid transparent conductors against a small bending radius or a repeated loading. Finally, organic light-emitting diodes based on the flexible metal grid transparent conductors are demonstrated. Our approach can open a new route to enhance the functionality of metallic structures fabricated using a variety of solution-processed metal patterning methods for next-generation optoelectronic and micro/nanoelectronic applications.

Effect of the anisotropy of etching surface morphology on light-trapping and photovoltaic conversion efficiencies of silicon solar cell

A homogeneous diamond wire sawing multicrystalline Si surface with nanoscale oval pits was obtained in an acid solution by adding NaNO2, polyethylene glycol–polyvinyl alcohol, and dodecylbenzene sulfonic acid at 12 °C for 130 s. The textured surface showed orientation dependence. The anisotropy of H/D caused different experimental results. The Rave of incident light originating from the direction parallel to saw marks was 22–27% larger than that from the direction perpendicular to saw marks. The photovoltaic conversion efficiency was 0.6–0.8% higher when the thin grid line of Ag electrode was parallel to the saw marks than when in the perpendicular direction. These results indicated that using saw marks can improve the conversion efficiency of solar cells.

Interaction dust – plasma in Titan's ionosphere: An experimental simulation of aerosols erosion

Organic aerosols accumulated in Titan's orange haze start forming in its ionosphere. This upper part of the atmosphere is highly reactive and complex ion chemistry takes place at altitudes from 1200 to 900 km. The ionosphere is a nitrogen plasma with a few percent of methane and hydrogen. Carbon from methane enables the formation of macromolecules with long organic chains, finally leading to the organic aerosols. On the other hand, we suspect that hydrogen and the protonated ions have a different erosive effect on the aerosols.Here we experimentally studied the effect of hydrogen and protonated species on organic aerosols. Analogues of Titan's aerosols were formed in a radiofrequency capacitively coupled plasma (RF CCP) discharge in 95% N2 and 5% CH4. Thereafter, the aerosols were exposed to a DC plasma in 99% N2 and 1% H2. Samples were analysed by scanning electron microscopy and in situ infrared transmission spectroscopy. Two pellet techniques – KBr pressed pellets and thin metallic grids - were compared to confirm that modifications seen are not due to the material used to make the pellet.We observed that the spherical aerosols of ~500 nm in diameter were eroded under N2-H2 plasma exposure, with the formation of holes of ~10 nm at their surface. Aerosols were globally removed from the pellet by the plasma. IR spectra showed a faster disappearance of isonitriles and/or carbo-diimides compared to the global band of nitriles. The opposite effect was seen with β-unsaturated nitriles and/or cyanamides. Double bonds as CC and CN were more affected than amines and CH bonds. NH and CH absorption bands kept a similar ratio in intensity and their shape did not vary.Therefore, it seems that carbon and hydrogen play opposite roles in Titan's ionosphere: the carbon from methane leads to organic growth while hydrogen and protonated species erode the aerosols and react preferentially with unsaturated chemical functions.

Influence of laser energy input on fabricating pure tungsten thin wall grids by selective laser melting

Pure tungsten thin wall grids were fabricated by selective laser melting. The effects of laser energy on formability, surface evenness, thickness, thickness deviation, relative density and microhardness of the fabricated grids were investigated and discussed. It was indicated that the grids were fabricated successfully with the linear energy density El in the range from 0.35 to 0.80 J mm−1. A higher or lower laser power and scanning rate increased the surface evenness of grids. For the design wall thicknesses of 0.15 and 0.20 mm, the fabricated grids with the thinnest wall thickness were about 0.27 and 0.32 mm, respectively. The thickness deviation of the grids reached a minimum of 0.02 mm. The relative density of the grid reached the maximum of 95.13%. The microhardness of the grid reached the maximum of 477.66 HV. El played an important effect on formability, surface evenness, thickness, thickness deviation, relative density and microhardness of the grids. Both a lower and higher El increased the thickness deviation, and decreased the microhardness and relative density of fabricated grids.