Large-scale 3D Structure Research Articles

High-precision and Large-Scale Vat Photopolymerization Printing based on "Spatial-Pixel Integration Compensation" method

Vat photopolymerization (VPP) is widely known for its exceptional printing accuracy, but effectively controlling stitching errors to achieve high-precision, large-scale printing remains a significant challenge. This study introduces a novel compensation method, termed "Spatial-Pixel Integration Compensation" (SPIC), to address this key obstacle. SPIC combines Spatial Motion Compensation to initially control stitching errors between adjacent sub-images to be within 100 µm and Pixel Compensation for precise adjustments, further reducing stitching errors. Integrating SPIC with our high-precision printing system resulted in a remarkable reduction of stitching errors by a factor exceeding 40. Crucially, this method minimizes the stitching error between any two sub-images to be less than one pixel point, specifically below 4 µm. Notably, SPIC is the first method specifically focused on effectively controlling and reducing stitching errors to achieve large-scale printing while maintaining high precision. To validate the practical applicability of the SPIC method, we used SPIC to print both Zig-Zag and herringbone structures (HBS) and achieved high-precision large-scale manufacturing with dimensions of 44 mm × 33 mm. In the HBS structure, the minimum feature size was 14.2 µm, and the printing error was less than 1 µm. These printed structures were used as molds to fabricate proof-of-concept polydimethylsiloxane (PDMS) microfluidic chips, demonstrating the successful mixing of rhodamine B and ethanol within the microfluidic channels. Furthermore, SPIC was extended to the printing of complex three-dimensional (3D) Triple-Periodic Minimal Surface (TPMS) structures, successfully producing TPMS-Gyroid and TPMS-Diamond structures with a minimum feature size of 20 µm and a printing error below 1.5 µm. These results demonstrate that the SPIC algorithm effectively enables high-precision, large-scale printing. This work significantly advances the application of VPP technology in fields requiring complex, high-precision, and large-scale 3D structures and provides valuable insights for future research in high-precision and large-scale printing.

Machining Surface Improvement through Electric- and Flow-Field Adjustments in Flying Electrochemical Milling of AA 2219.

Electrochemical milling is an ideal technique for machining large-scale 3D structures that consist of aerospace aluminum alloys. The distribution of the electric and flow fields are vital to the quality of the machined surface, and the structures of the inner flow channel and bottom outlet have different effects on the electric and flow fields on the machining surface. In this study, two specialized structures of a tool cathode were optimized by simulating the electric and flow fields, and a reasonable design basis for the tool cathode was obtained. Based on this, an ECM experiment was performed with the same machining parameters using different tools, and a 20 mm × 20 mm plane was machined. The experimental results showed that using an appropriate tool cathode can create ideal flow and electric fields, resulting in better processing. After optimizing, the machining plane arithmetic mean deviation decreased by 43% (from 14.050 μm to 6.045 μm), and the region elevation difference decreased by 52% (from 105.93 μm to 55.17 μm).

Parallel two-photon lithography achieving uniform sub-200 nm features with thousands of individually controlled foci.

The limited throughput of nano-scale laser lithography has been the bottleneck for its industrial applications. Although using multiple laser foci to parallelize the lithography process is an effective and straightforward strategy to improve rate, most conventional multi-focus methods are plagued by non-uniform laser intensity distribution due to the lack of individual control for each focus, which greatly hinders the nano-scale precision. In this paper, we present a highly uniform parallel two-photon lithography method based on a digital mirror device (DMD) and microlens array (MLA), which allows the generation of thousands of femtosecond (fs) laser foci with individual on-off switching and intensity-tuning capability. In the experiments, we generated a 1,600-laser focus array for parallel fabrication. Notably, the intensity uniformity of the focus array reached 97.7%, where the intensity-tuning precision for each focus reached 0.83%. A uniform dot array structure was fabricated to demonstrate parallel fabrication of sub-diffraction limit features, i.e., below 1/4 λ or 200 nm. The multi-focus lithography method has the potential of realizing rapid fabrication of sub-diffraction, arbitrarily complex, and large-scale 3D structures with three orders of magnitude higher fabrication rate.

Hydraulic and statistical study of metastable phenomena in PWR rod bundles

The analysis of fuel rod bundle flows constitutes a key element of Pressurized-Water Reactors (PWR) safety studies. The present work aims at improving our understanding of nefarious reorganisation phenomena observed by numerous studies in the flow large-scale structures. 3D simulations allowed identifying two distinct reorganisations consisting in a sign change for either a transverse velocity in rod-to-rod gaps or for a subchannel vortex. A Taylor “frozen turbulence” hypothesis was adopted to model the evolution of large-scale 3D structures as transported-2D. A statistical method was applied to the 2D field to determine its thermodynamically stable states through an optimization problem. Similarities were obtained between the PWR coherent structures and the stable states in a simplified 2D geometry. Further, 2D simulations allowed identifying two possible flow bifurcations, each related to one of the reorganisations observed in 3D simulations, laying the foundations for a physical explanation of this phenomenon.

THREE-DIMENSIONAL DISTRIBUTION OF EJECTA IN SUPERNOVA 1987A AT 10,000 DAYS

ABSTRACT Due to its proximity, SN 1987A offers a unique opportunity to directly observe the geometry of a stellar explosion as it unfolds. Here we present spectral and imaging observations of SN 1987A obtained ∼10,000 days after the explosion with HST/STIS and VLT/SINFONI at optical and near-infrared wavelengths. These observations allow us to produce the most detailed 3D map of Hα to date, the first 3D maps for [Ca ii] , [O i] , and Mg ii , as well as new maps for [Si i]+[Fe ii] and He i 2.058 μm. A comparison with previous observations shows that the [Si i]+[Fe ii] flux and morphology have not changed significantly during the past ten years, providing evidence that this line is powered by 44Ti. The time evolution of Hα shows that it is predominantly powered by X-rays from the ring, in agreement with previous findings. All lines that have sufficient signal show a similar large-scale 3D structure, with a north–south asymmetry that resembles a broken dipole. This structure correlates with early observations of asymmetries, showing that there is a global asymmetry that extends from the inner core to the outer envelope. On smaller scales, the two brightest lines, Hα and [Si i]+[Fe ii] 1.644 μm, show substructures at the level of ∼200–1000 km s–1and clear differences in their 3D geometries. We discuss these results in the context of explosion models and the properties of dust in the ejecta.

Prediction of etching-shape anomaly due to distortion of ion sheath around a large-scale three-dimensional structure by means of on-wafer monitoring technique and computer simulation

A system for predicting distortion of a profile during plasma etching was developed. The system consists of a combination of measurement and simulation. An ‘on-wafer sheath-shape sensor’ for measuring the plasma-sheath parameters (sheath potential and thickness) on the stage of the plasma etcher was developed. The sensor has numerous small electrodes for measuring sheath potential and saturation ion-current density, from which sheath thickness can be calculated. The results of the measurement show reasonable dependence on source power, bias power and pressure. Based on self-consistent calculation of potential distribution and ion- and electron-density distributions, simulation of the sheath potential distribution around an arbitrary 3D structure and the trajectory of incident ions from the plasma to the structure was developed. To confirm the validity of the distortion prediction by comparing it with experimentally measured distortion, silicon trench etching under chlorine inductively coupled plasma (ICP) was performed using a sample with a vertical step. It was found that the etched trench was distorted when the distance from the step was several millimetres or less. The distortion angle was about 20° at maximum. Measurement was performed using the on-wafer sheath-shape sensor in the same plasma condition as the etching. The ion incident angle, calculated as a function of distance from the step, successfully reproduced the experimentally measured angle, indicating that the combination of measurement by the on-wafer sheath-shape sensor and simulation can predict distortion of an etched structure. This prediction system will be useful for designing devices with large-scale 3D structures (such as those in MEMS) and determining the optimum etching conditions to obtain the desired profiles.

Gauge-SURF descriptors

In this paper, we present a novel family of multiscale local feature descriptors, a theoretically and intuitively well justified variant of SURF which is straightforward to implement but which nevertheless is capable of demonstrably better performance with comparable computational cost. Our family of descriptors, called Gauge-SURF (G-SURF), is based on second-order multiscale gauge derivatives. While the standard derivatives used to build a SURF descriptor are all relative to a single chosen orientation, gauge derivatives are evaluated relative to the gradient direction at every pixel. Like standard SURF descriptors, G-SURF descriptors are fast to compute due to the use of integral images, but have extra matching robustness due to the extra invariance offered by gauge derivatives. We present extensive experimental image matching results on the Mikolajczyk and Schmid dataset which show the clear advantages of our family of descriptors against first-order local derivatives based descriptors such as: SURF, Modified-SURF (M-SURF) and SIFT, in both standard and upright forms. In addition, we also show experimental results on large-scale 3D Structure from Motion (SfM) and visual categorization applications.

3D cartographic modeling of the Alpine arc

We built a 3D cartography of the Alpine arc, a highly non-cylindrical mountain belt, using the 3D GeoModeller of the BRGM (French geological survey). The model allows to handle the large-scale 3D structure of seventeen major crustal units of the belt (from the lower crust to the sedimentary cover nappes), and two main discontinuities (the Insubric Line and the Crustal Penninic Front). It provides a unique document to better understand their structural relationships and to produce new sections. The study area comprises the western Alpine arc, from the Jura to the Northwest, up to the Bergell granite intrusion and the Lepontine Dome to the East, and is limited to the South by the Ligurian basin. The model is limited vertically 10km above sea level at the top, and the moho interface at the bottom. We discarded the structural relationships between the Alps sensus stricto and the surrounding geodynamic systems such as the Rhine graben or the connection with the Apennines. The 3D-model is based on the global integration of various data such as the DEM of the Alps, the moho isobaths, the simplified geological and tectonic maps of the belt, the crustal cross-sections ECORS-CROP and NFP-20, and complementary cross-sections specifically built to precise local complexities. The database has first been integrated in a GIS-project to prepare their implementation in the GeoModeller, by homogenizing the different spatial referencing systems. The global model is finally interpolated from all these data, using the potential field method. The final document is a new tri-dimensional cartography that would be used as input for further alpine studies.

A three-dimensional continuum approach to the thermoelastodynamics of large-scale structures

A three-dimensional (3D) continuum procedure proposed for the evaluation of the temperature field due to solar and environmental exposure in large-scale 3D structures, together with effects on the linear modal properties is here. 3D finite element discretization of the heat equation is employed to compute first, the temperature changes in the structure due to the heat exchanges with the external environment. The heat equation is complemented with nonlinear boundary conditions of the Fourier–Robin type to describe heat transfers by convection, radiation, and solar radiation. The heat exchanges by convection and radiation between the structure and the surrounding air are described once the variation of air temperature with time is known. The solar radiation on the structure is defined through a procedure that requires, as input data, the geometry and the orientation of the irradiated surfaces, the latitude of the location, and the clearness index. The computed thermal fields represent the input data for the nonlinear problem which governs the thermoelastic equilibrium. The linearization of the equations of motion about this equilibrium state yields the eigenvalue problem governing the evolution of the eigenfrequencies due to the slowly time-varying thermal gradients. A nonlinear continuum model based on a linearly elastic constitutive law is employed. The novelty of this work lies in the accurate description of the thermal gradient field, in terms of the actual measurable input data to the heat diffusion problem, as well as the refined mechanical representation of the 3D effects of the thermo-geometric stiffness and the elastic moduli.

The large scale magnetic field structure of the spiral galaxy NGC 5775

In order to better determine the large-scale 3D-structure of magnetic fields in spiral galaxies we present a Faraday rotation analysis of the edge-on spiral galaxy NGC 5775. Deep radio-continuum observations in total power and linear polarization were performed at 8.46 GHz with the VLA and the 100-m Effelsberg telescope. They were analyzed together with archival 4.86 and 1.49 GHz VLA-data. We thus can derive rotation measures from a comparison of three frequencies and determine the intrinsic magnetic field structure. A very extended halo is detected in NGC 5775, with magnetic field lines forming an X-shaped structure. Close to the galactic disk the magnetic field is plane-parallel. The scaleheights of the radio emission esimated for NGC 5775 are comaprable with other galaxies. The rotation measure distribution varies smoothly on both sides along the major axis from positive to negative values. From the derived distribution of rotation measures and the plane-parallel intrinsic magnetic field orientation along the galactic midplane we conclude that NGC 5775 has an 'even axisymmetric' large-scale magnetic field configuration in the disk as generated by an \alpha \Omega -dynamo which is accompanied by a quadrupolar poloidal field. The magnetic field lines of the plane-parallel component are pointing 'outwards'. The observed X-shaped halo magnetic field, however, cannot be explained by the action of the disk's mean-field dynamo alone. It is probably due to the influence of the galactic wind together with the dynamo action.

In vitro culture of large bone substitutes in a new bioreactor: importance of the flow direction

New biomaterials combined with osteogenic cells are now being developed as an alternative to autogeneous bone grafts when the skeletal defect reaches a critical size. Yet, the size issue appears to be a key obstacle in the development of bone tissue engineering. Bioreactors are needed to allow the in vitro expansion of cells inside large bulk materials under appropriate conditions. However, no bioreactor has yet been designed for large-scale 3D structures and custom-made scaffolds. In this study, we evaluate the efficiency of a new bioreactor for the in vitro development of large bone substitutes, ensuring the perfusion of large ceramic scaffolds by the nutritive medium. The survival and proliferation of cells inside the scaffolds after 7 and 28 days in this dynamic culture system and the impact of the direction of the flow circulation are evaluated. The follow-up of glucose consumption, DNA quantification and microscopic evaluation all confirmed cell survival and proliferation for a sample under dynamic culture conditions, whereas static culture leads to the death of cells inside the scaffolds. Two directions of flow perfusion were assayed; the convergent direction leads to enhanced results compared to divergent flow.

Computing a new family of shape descriptors for protein structures.

The large-scale 3D structure of a protein can be represented by the polygonal curve through the carbon alpha atoms of the protein backbone. We introduce an algorithm for computing the average number of times that a given configuration of crossings on such polygonal curves is seen, the average being taken over all directions in space. Hereby, we introduce a new family of global geometric measures of protein structures, which we compare with the so-called generalized Gauss integrals.