Single Cube Research Articles

Process parameter optimization for selective laser melting Ti-6Al-4V with high layer thickness

Increasing the layer thickness is an important method to increase the forming efficiency of selective laser melting (SLM) but affects the forming quality. In this work, a single track and cube sample with an 80µm layer thickness was fabricated by SLM, and then the relative density, hardness, defects, and forming efficiency were studied. It is found that the morphology of the single tracks changes significantly with the change of scanning speed. Fewer defects appear on the top surface and cross section with scanning speed below 850mm/s. However, the defects increase significantly with further increasing scanning speed. Furthermore, the relative density of the Ti-6Al-4V can reach 99.89% when the scanning speed is 800mm/s. The Vickers hardness is highest when the scanning speed is 500mm/s with the top surface of 402 HV and the side surface of 378 HV. An increase of scanning speed not only causes larger balling particles, but also results in making an appearance of micro-cracks. The increase in layer thickness leads to insufficient energy density, which affects the occurrence of lack of fusion concurrently. Element evaporation occurs at low scanning speeds, which can increase defects in the sample. The appropriate process parameters are the laser power of 300W, the scanning speed of 800mm/s, and hatch distance of 0.17mm. At this time, the forming efficiency is as high as 8.96 mm3/s.

High strain-rate strength response of single crystal tantalum through in-situ hole closure imaging experiments

The properties of crystalline materials often depend on directionality and operating conditions. Specifically, the strength of materials can depend anisotropically on crystal direction and the loading condition. To probe these effects, a preliminary series of high strain-rate (>105/s) strength plate-impact hole closure experiments were performed on high purity single crystal tantalum cubes. The orientation of the single crystals with respect to impact/loading were varied to provide data to inform crystal plasticity modeling efforts. The experiments consist of in-situ high-resolution X-ray radiographic imaging of the hole collapse under dynamic compression conditions to infer the material strength via its resistance to closure at increasing levels of plastic strain. The experiments are compared against hydrocode simulation predictions. A comparison with simple elastic perfectly plastic strength model predictions is presented to elucidate the response of the different crystal orientations at high strain-rate and large plastic strains.

Promoted oxygen adsorption on porous CeO2 cubes with abundant oxygen vacancies for efficient gaseous formaldehyde removal

Photocatalytic degradation stands as a promising method for eliminating gas-phase pollutants, with the efficiency largely hinging on the capture of photogenerated electrons by oxygen. In this work, we synthesized a porous CeO2 single crystal cube with abundant oxygen vacancies as photocatalyst, employing urea as a pore-forming agent and for gas-phase formaldehyde degradation. Compared with the CeO2 cubes without pores, the porous ones were superior in specific surface area, akin to conventional CeO2 nanoparticles. The photocatalytic degradation for gas-phase formaldehyde on porous CeO2 cubes was significantly accelerated, of which degradation rate is 3.3 times and 2.1 times that of CeO2 cubes without pores and CeO2 nanoparticles, respectively. Photoelectric tests and DFT calculations revealed that this enhancement stemmed from facilitated oxygen adsorption due to pronounced oxygen vacancies. Consequently, the capture of photoelectrons by oxygen was promoted and its recombination with holes was suppressed, along with an accelerated generation of curial free radicals such as ·OH. This work reveals the pivotal role of surface oxygen vacancies in promoting adsorbed oxygen, proposing a viable strategy to enhance the photocatalytic degradation efficiency for gas-phase pollutants.

Large-Eddy Simulations of Flow over a Backward-Facing Ramp with a Wall-Mounted Cube

Passive flow control devices, such as vortex generators (VGs), can effectively modulate the turbulent boundary layer flow near regions of adverse pressure gradients, but the interactions between the salient flow structures produced by VGs and those of the separated flow are not fully understood. In this study, a spatially evolving turbulent boundary layer interacting with a wall-mounted cube ahead of a backward-facing ramp is investigated using wall-resolved large-eddy simulations for a Reynolds number of 19,600, based on the inlet boundary layer thickness and freestream velocity. Different cube configurations are examined to isolate the effects of cube height and streamwise position. The large counter-rotating flow produced by the larger cubes generated more turbulent kinetic energy, thereby resulting in smaller separated regions over the ramp. Although significantly lower levels of turbulent kinetic energy dissipation than production are observed in the outer flow regions of the horseshoe vortex and in the induced counter-rotating flow, the spatial distribution of dissipation is similar to that of the turbulent kinetic energy. When the upstream position of an isolated single cube, relative to the leading ramp edge, is more than three cube heights, the streamwise decay of the counter-rotating flow results in lower levels of turbulent kinetic energy.

Self-assembled nano-MnS@N,P dual-doped lignite based carbon as high-performance sodium-ion batteries anode

Manganese sulfide (MnS) is a suitable electrode material for use in sodium-ion batteries (SIBs) due to its high theoretical capacity and low cost. However, its practical application is still hampered by disadvantages such as large volume expansion during charging/discharging and limited cycle life. Therefore, reasonable structural design is of great importance in order to achieve an excellent sodium storage performance of the electrode materials for SIBs. Herein, nano-MnS@N,P dual-doped lignite based porous carbon (MnS@N,P-LPC) composite with a single MnS cube encapsulated in an N,P dual-doped lignite derived porous C is successfully prepared as superior anode material for SIBs. The multilayer pore structure and the combined effect of N and P dual-doping can enhance electrochemical performance by supplying more sodium storage sites. After 200 cycles at 0.1 A g−1, the composite complex produced a maximum capacity of 519 mA h g−1 and demonstrated a capacity of 392.5 mA h g−1 even at 1.6 A g−1. It exhibits outstanding cycling stability and superior rate performance. This excellent electrochemical performance is ascribed to the presence of the multilayer pore N,P dual-doped C skeleton, which effectively addresses the volume expansion of MnS particles during charging/discharging and facilitates efficient transport of ions and electrons through an effective conductive network.

Robust self-propulsion in sand using simply controlled vibrating cubes.

Much of the Earth and many surfaces of extraterrestrial bodies are composed of non-cohesive particulate matter. Locomoting on such granular terrain is challenging for common robotic devices, either wheeled or legged. In this work, we discover a robust alternative locomotion mechanism on granular media-generating movement via self-vibration. To demonstrate the effectiveness of this locomotion mechanism, we develop a cube-shaped robot with an embedded vibratory motor and conduct systematic experiments on granular terrains of various particle properties and slopes. We investigate how locomotion changes as a function of vibration frequency/intensity on such granular terrains. Compared to hard surfaces, we find such a vibratory locomotion mechanism enables the robot to move faster, and more stably on granular surfaces, facilitated by the interaction between the body and surrounding grains. We develop a numerical simulation of a vibrating single cube on granular media, enabling us to justify our hypothesis that the cube achieves locomotion through the oscillations excited at a distance from the cube's center of mass. The simplicity in structural design and controls of this robotic system indicates that vibratory locomotion can be a valuable alternative way to produce robust locomotion on granular terrains. We further demonstrate that such cube-shaped robots can be used as modular units for vibratory robots with capabilities of maneuverable forward and turning motions, showing potential practical scenarios for robotic systems.

Macroscopic emulation of microscopic magnetic particle systems

In this work we show that macroscopic experiments can be used to investigate microscopic systems. Such macroscopic experiments enable testing the assumptions and results obtained by theoretical considerations or simulations that cannot be obtained under microscope (e.g., the orientation of a spherical particle).To emulate the dynamics of a single hematite cube immersed in water and subjected to a rotating magnetic field, a cubic magnet is firmly positioned in a 3D printed superball shell. The dimensionless parameters of the microscopic and macroscopic systems can be equalized by using a glycerol-water mixture instead of water as well as by the material and infill of the 3D printed shell. The pose of the superball is tracked using ArUco stickers which act as fiducial markers.It was found that there is a qualitative agreement between the macroscopic experiments and theoretical predictions. However, the reduced thermal effects in the macroscopic experiments lead to an increase in friction between the superball and the surface, thus shifting the critical frequency of the system.Since the shell is 3D printed, the given method can be extended to any shape and magnetization orientation.

Cracking mechanisms in additively manufactured pure tungsten from printing single tracks, thin walls and cubes

Cracking is a critical issue in the additive manufacturing of pure tungsten (W). To eliminate crack formation, it is imperative to gain an in-depth understanding of the underlying mechanisms behind this process. In this study, we systematically investigated the crack behaviors of single tracks, thin walls, and cubes fabricated using powder bed fusion–laser beam (PBF–LB) technology with nonrotational parallel-hatching scanning. The energy framework was employed to elucidate the mechanism of crack formation. The longitudinal cracks appearing in the microstructures of single tracks and the through cracks existing in thin walls and cubes were characterized. Notably, periodic through cracks extended upward across the sample, appearing at every single hatch in unidirectional samples and at every other hatch in bidirectional samples. The horizontal, longitudinal, and transverse cross sections of cubes were studied to clarify the correlation between through crack arrangement and solidification microstructure. Based on a comprehensive analysis of grain boundaries, we proposed a deformation-cracking competition mechanism in PBF–LB tungsten. Geometric effects in the crack and microstructure were also revealed. This study could provide valuable insights into the formation of cracks in PBF–LB tungsten and serve as a foundation for future investigations aimed at eliminating cracks.

Rotating hematite cube chains.

Recently a two-dimensional chiral fluid was experimentally demonstrated. It was obtained from cubic-shaped hematite colloidal particles placed in a rotating magnetic field. Here we look at building blocks of that fluid by analyzing short hematite chain behavior in a rotating magnetic field. We find equilibrium structures of chains in static magnetic fields and observe chain dynamics in rotating magnetic fields. We find and experimentally verify that there are three planar motion regimes and one where the cube chain goes out of the plane of the rotating magnetic field. In this regime we observe interesting dynamics-the chain rotates slower than the rotating magnetic field. In order to catch up with the magnetic field, it rolls on an edge and through rotation in the third dimension catches up with the magnetic field. The same dynamics is also observable for a single cube when gravitational effects are explicitly taken into account.

Electric- and magnetic-dipole surface lattice resonances in microwave regime

At optical frequencies, the collective excitation of the periodic array of metallic meta-molecules can support surface lattice resonances (SLRs) due to the coupling of localized surface-plasmon (LSP) resonances to Rayleigh anomaly diffraction. However, the LSP effect in metal blocks becomes negligible in the microwave region. Thus, how the SLRs behave in the microwave regime is very interesting. In this paper, a microwave metasurface consisting of periodic metallic cubes on an ultrathin dielectric substrate is investigated. Two high-Q transmission dips are found, which can be attributed, respectively, to electric-dipole SLRs (ED-SLRs) and magnetic-dipole SLRs (MD-SLRs), because of the non-resonant Rayleigh-like scattering of single cubes and diffraction coupling of the periodic array. The frequencies of both ED- and MD-SLRs are sensitive to the refractive index of the substrate, suggesting that the proposed metasurface may be used to measure the refractive index in the microwave range.

Effect of Neutrinos on Angular Momentum of Dark Matter Halo

Massive neutrinos are expected to affect the large-scale structure formation, including the major component of solid substances, dark matter halos. How halos are influenced by neutrinos is vital and interesting, and angular momentum (AM) as a significant feature provides a statistical perspective for this issue. Exploring halos from TianNu N-body cosmological simulation with the co-evolving neutrino particles, we obtain some concrete conclusions. First, by comparing the same halos with and without neutrinos, in contrast to the neutrino-free case, over 89.71% of halos have smaller halo moduli, over 71.06% have smaller particle-mass-reduced (PMR) AM moduli, and over 95.44% change their orientations of less than 0.°65. Moreover, the relative variation of PMR modulus is more visible for low-mass halos. Second, to explore the PMR moduli of halos in dense or sparse areas, we divide the whole box into big cubes, and search for halos within a small spherical cell in a single cube. From the two-level divisions, we discover that in denser cubes, the variation of PMR moduli with massive neutrinos decreases more significantly. This distinction suggests that neutrinos exert heavier influence on halos’ moduli in compact regions. With massive neutrinos, most halos (86.60%) have lower masses than without neutrinos.

OPTIMAL DESIGN BY MASS FOR TRANSMISSION OF TRACKED LOAD-CARRIER/PRIME MOVER MT-LB: MATHEMATICAL MODEL, ALGORITHM, NUMERICAL EXPERIMENT

Solving the problem of optimizing for transmission of light multipurpose tracked load-carrier/prime mover MT-LB is a perspective area of research because it improves the mass characteristics of the machine, to ensure the load capacity and durability of transmission at upgrading. Mathematical model of transmission optimization by mass was constructed, namely: optimization objective function of transmission by weight was built, which is quite correct transmission models, it takes into account the geometry, dimensions, weight and strength properties of the main parts and aggregates; variables planning are defined, which selected as basic geometric parameters of gearings (modules and number of teeth); a system of constraints on the variables planning was constructed, a technique for dynamically changing the constraints on the teeth number for gearbox was proposed. A sequence of constraint checking is proposed, which will reduce the amount and time of calculations to find the best solution. The solution is based on sensing the parameter space, where points of the LPτ-sequence are used as test points in a single multidimensional cube. Also, the applied methodology and detailed algorithm for optimal design of the transmission has been developed. They take into account the constructive, technical and technological features. They also allow to reduce the error of the calculations due to the error-control of the calculations of gear ratios and the equality of the axes distance for gearbox and additional reducer meshing's. A number of numerical experiments were carried out for the base engine and the other 4 engines. The analysis of the results makes it possible to conclude that a significant reduction in the weight and dimensions of the transmission has been achieved compared to the basic one at loads corresponding to typical driving modes. Keywords: optimal design, multipurpose load-carrier/prime mover MT-LB, transmission, mathematical model, objective function, variables planning, algorithm

LOFAR Deep Fields: Probing faint Galactic polarised emission in ELAIS-N1

We present the first deep polarimetric study of Galactic synchrotron emission at low radio frequencies. Our study is based on 21 observations of the European Large Area Infrared Space Observatory Survey-North 1 (ELAIS-N1) field using the Low-Frequency Array (LOFAR) at frequencies from 114.9 to 177.4 MHz. These data are a part of the LOFAR Two-metre Sky Survey Deep Fields Data Release 1. We used very low-resolution (4.3′) Stokes QU data cubes of this release. We applied rotation measure (RM) synthesis to decompose the distribution of polarised structures in Faraday depth, and cross-correlation RM synthesis to align different observations in Faraday depth. We stacked images of about 150 h of the ELAIS-N1 observations to produce the deepest Faraday cube at low radio frequencies to date, tailored to studies of Galactic synchrotron emission and the intervening magneto-ionic interstellar medium. This Faraday cube covers ~36 deg2 of the sky and has a noise of 27 µJy PSF−1 RMSF−1 in polarised intensity. This is an improvement in noise by a factor of approximately the square root of the number of stacked data cubes (~√20), as expected, compared to the one in a single data cube based on five-to-eight-hour observations. We detect a faint component of diffuse polarised emission in the stacked cube, which was not detected previously. Additionally, we verify the reliability of the ionospheric Faraday rotation corrections estimated from the satellite-based total electron content measurements to be of ~0.05 гad m−2. We also demonstrate that diffuse polarised emission itself can be used to account for the relative ionospheric Faraday rotation corrections with respect to a reference observation.

Single-longitudinal-mode Ho:YLF unidirectional ring laser with single anti-misalignment corner cube retroflector

A single-longitudinal-mode Ho:YLF unidirectional ring laser with single anti-misalignment corner cube retroflector (CCR) for providing the stable local oscillator to 2.05 μm laser lidar was demonstrated in this paper. The single-longitudinal-mode output power of 569 mW at 2051.76 nm was obtained by inserting a half-wave plate and a Faraday rotator to the ring oscillator. The output wavelength was tuned from 2050.94 nm to 2054.18 nm through a 0.3-mm-thick F-P etalon, which close to the free spectrum range of the etalon. In addition, the anti-misalignment characteristic of the unidirectional ring laser was investigated when the single CCR moved along the optical axis and perpendicular to the optical axis. The beam quality factors M2 of the Ho:YLF single-longitudinal-mode laser were 1.05 in the x direction and 1.02 in the y direction, respectively.

Weather-driven synergistic water-economy-environment regulation of farmland ecosystems

Farmland ecosystems (FEs) constitute the most important source of food production, and water is one of the most important factors influencing FEs. The amount of water can affect the yield and thus the economic efficiency. Water migration can generate environmental effects through the migration of fertilizers. Interlinkages and constraints exist between the water, economy and environment, which require synergistic regulation. Meteorological elements influence the reference crop uptake amount and thus the water cycle processes and are key drivers of regulation at the water-economy-environment nexus. However, the weather-driven, synergistic water-economy-environment regulation of FEs has not been sufficiently researched. As such, this paper employed a dynamic Bayesian prediction of the reference evapotranspiration (ETo) and a quantitative characterization of the total nitrogen (TN) and total phosphorus (TP) contents in agricultural crops and soils via field monitoring and indoor experimental analysis. Consequently, multiobjective optimization modeling was conducted to weigh the mutual trade-offs and constraints between water, the economy and the environment. The proposed method was verified via an example involving the modern agricultural high-tech demonstration park in Harbin, Heilongjiang Province, China. The results indicated that (1) the effect of meteorological factors gradually decreased over time, but the prediction results were very accurate, and the higher the delay order of the dynamic Bayesian network (DBN) was, the more accurate the predictions; (2) ETo was significantly driven by meteorological elements, and the most important meteorological factor influencing ETo throughout the year was average temperature. When the average temperature was reduced by 10.0 %, ETo was reduced by 1.4 %, the required amount of irrigation water was reduced by 4.9 %, and the economic benefits of a single cube of water increased by 6.3 %; (3) resource-economy-environment multidimensional synergy enabled a 12.8 % reduction in agricultural ecosystem pollutant emissions, while the economic benefits per unit of water increased by 8.2 % and the system synergy increased by 23.2 %.

CTIS-GAN: computed tomography imaging spectrometry based on a generative adversarial network.

Computed tomography imaging spectrometry (CTIS) is a snapshot hyperspectral imaging technique that can obtain a three-dimensional (2D spatial+1D spectral) data cube of the scene captured within a single exposure. The CTIS inversion problem is typically highly ill-posed and is usually solved by time-consuming iterative algorithms. This work aims to take the full advantage of the recent advances in deep-learning algorithms to dramatically reduce the computational cost. For this purpose, a generative adversarial network is developed and integrated with self-attention, which cleverly exploits the clearly utilizable features of zero-order diffraction of CTIS. The proposed network is able to reconstruct a CTIS data cube (containing 31 spectral bands) in milliseconds with a higher quality than traditional methods and the state-of-the-art (SOTA). Simulation studies based on real image data sets confirmed the robustness and efficiency of the method. In numerical experiments with 1000 samples, the average reconstruction time for a single data cube was ∼16m s. The robustness of the method against noise is also confirmed by numerical experiments with different levels of Gaussian noise. The CTIS generative adversarial network framework can be easily extended to solve CTIS problems with larger spatial and spectral dimensions, or migrated to other compressed spectral imaging modalities.

Pulsed Er:YAG single corner cube ring cavity with variable output ratio

In this paper, a ring cavity of Er:YAG laser with a single corner cube prism is investigated. Due to the depolarization effect of the corner cube, the tunable output coupling ratio was 0.25% to 72.67% by changing the angle of the λ / 4 plate according to the calculation results of Jones matrix. An experiment for checking the anti-detuning performances of the single corner cube cavity was also carried out. The results indicated that the output power was stable at the rotating angles of <3.06 deg and 1.637 deg along the vertical and horizontal directions, respectively. Under continuous wave operation, a 5.4 W vertically-polarized laser of 1645.1 nm was acquired through double polarizers with the beam quality factors (M2) of 1.17 in the x direction and 1.42 in the y direction, and the slope efficiency was 45.47%. Additionally, under the condition of a pulse-repetition-frequency (PRF) of 200 Hz, the pump power of 29.04 W, a maximum pulse energy of 2.2 mJ was realized, and the minimum pulse width was 86 ns, leading to a peak power of 25.58 KW.

Kernel Density Derivative Estimation of Euler Solutions

Conventional Euler deconvolution is widely used for interpreting profile, grid, and ungridded potential field data. The Tensor Euler deconvolution applies additional constraints to the Euler solution using all gravity vectors and the full gravity gradient tensor. These algorithms use a series of different-sized moving windows to yield many solutions that can be employed to estimate the source location from the entire survey area. However, traditional discrimination techniques ignore the interrelation among the Euler solutions, so they cannot be employed to separate adjacent targets. To overcome this difficulty, we introduced multivariate Kernel Density Derivative Estimation (KDDE) as an extension of Kernel Density Estimation, which is a mathematical process to estimate the probability density function of a random variable. The multivariate KDDE was tested on a single cube model, a single cylinder model, and three composite models consisting of two cubes with various separations using gridded data. The probability value calculated by the multivariate KDDE was used to discriminate spurious solutions from the Euler solution dataset and isolate adjacent geological sources. The method was then applied to airborne gravity data from British Columbia, Canada. Then, the results of synthetic models and field data show that the proposed method can successfully locate meaningful geological targets.

A Method for Turning a Single Low-Cost Cube into a Reference Target for Point Cloud Registration

Target-based point cloud registration methods are still widely used by many laser scanning professionals due to their direct and manipulable nature. However, placing and moving multiple targets such as spheres for registration is a time-consuming and tactical process. When the number of scans gets large, the time and labor costs will accumulate to a high level. In this paper, we propose a flexible registration method that requires the installation of only a low-cost cubical target: a die-like object. The method includes virtual coordinate system construction and two error compensation techniques, in which the non-orthogonality of the scanned facets, along with the unknown sizes of the dice are estimated based on projection geometry and cubical constraints so that three pairs of conjugate points can be accurately identified along the axes of the constructed coordinate systems for the registration. No scan overlap of the facet is needed. Two different low-cost dice (with a volume of 0.125 m3 and 0.027 m3) were used for verifying the proposed method, which shows that the proposed method delivers registration accuracy (with an RMSE discrepancy of less than 0.5 mm for check planes) comparable to the traditional sphere- based method using four to six spherical targets spanning the scene. Therefore, the proposed method is particularly useful for registering point clouds in harsh scanning environments with limited target-setting space and high chances of target interruption.

Melting modes of laser powder bed fusion (L-PBF) processed IN718 alloy: Prediction and experimental analysis

The present study explores a combination of numerical and simulation approaches to generate a process map for identifying the regimes of conduction and keyhole modes of melting and verify the same with experimental data. Finite Element based simulation studies were conducted to determine the regions of conduction mode, keyhole mode, and transition by varying the laser power and speed. Single tracks and density cubes were processed based on the simulation results to confirm the melting modes and study its effect on microstructure and hardness. Increase in volumetric energy density (VED) causes a shift in microstructure of single tracks, from a mix of short columnar and equiaxed grains in conduction mode to long columnar grains in keyhole mode, with an overall increase in the grain size. The melt pool depth to width ratio also increases with VED. The VED based criteria alone cannot determine melting modes as the single-track samples at 81 J/mm3 exhibited both conduction mode (at 250 W) and keyhole mode (at 350 W). Almost all the printed cubes showed high density (>99.9%) irrespective of melting mode. Similar to single track the average grain size of bulk samples increased with increase in VED. The bulk samples were subjected to three different heat treatments (Homogenisation, Solution treatment and Direct Double Aging) to study their effect on the microstructures and mechanical properties. Homogenisation resulted in near identical equiaxed microstructure irrespective of processing parameters. The highest hardness of about 470 HV was observed for the direct double aged samples.