3-cube Research Articles

Integrating Scientific Approaches in Digital Learning Materials to Improve Spatial Abilities in Cube Geometry: A Research and Development

This research aims to determine the level of validity, practicality and effectiveness of digital teaching materials based on a scientific approach, so that they can improve students' spatial abilities in cube material. This type of research is development research with the ADDIE development model. Research instruments in the research include questionnaire validation sheets, lesson plan validation sheets, digital teaching material validation sheets, test instrument validation sheets, spatial ability tests, as well as teacher and student response questionnaires to digital teaching materials. The research results show that: (1) the scientific approach-based digital teaching materials developed have met the validity criteria based on validator assessments with the average validity of digital teaching materials for material being 3.44 and 3.82 for media in the very appropriate category; (2) the scientific approach-based digital teaching materials developed have met the practicality criteria through: a) the results of the student response questionnaire to digital teaching materials show a practicality percentage of 82.75% in the very practical category, b) the results of the teacher response questionnaire to digital teaching materials show practicality percentage 91.67% in the very practical category; (3) The scientific approach-based digital teaching materials developed meet the effective criteria with: a) classical student learning completeness of 90%, b) more than 65% of students have achieved 75% of the learning objectives for each indicator, c) increasing students' spatial abilities After using digital teaching materials, it can be seen from the students' average score increasing from 47.67 in the pretest to 86.50 in the posttest. The results of the N-Gain analysis which shows that students' spatial abilities have increased by 0.725, meaning they are in the high category.

Gradient ceramic structures via multi-material direct ink writing

Dense boron carbide-silicon carbide specimens with composition tailored at the mesoscale were produced by direct ink write additive manufacturing in three configurations: I, 2 % and II, 10 % compositional layer-to-layer steps, and III, homogeneous composition throughout. Flexural strength, indicative of tensile failure, is the highest for the Type-II design (366 MPa) due to its compressive residual stress state in the surface layers. Analysis of thermally-induced residual stresses predicts the ranking of the flexural strengths obtained for Type-II (highest), Type-I (intermediate), and Type-III (lowest) specimens. Compressive strength is load-orientation independent, highly strain-rate dependent, and reduced for specimens with thermal residual stress. Mechanical tests were performed in cube and dumbbell geometries. Dumbbell geometry compression specimens have a compressive strength that is 68 % (quasistatic) and 86 % (dynamic) higher than that of cube geometry and show a greater strain rate dependence. The rate dependency is attributed to the competition between crack propagation and loading velocities. Type-I dumbbells show the highest mean compressive strength of 3.96 GPa (quasi-static) and 5.11 GPa (dynamic). The failure mode evolves from mixed intergranular/transgranular at low strain rates to transgranular at high strain rates. High-speed video analysis indicates that dumbbell geometry specimens fail in compression due to microcrack growth and coalescence, while cubes fail due to the axial macrocracks that develop at the specimen/load platen interface and propagate into the specimen parallel to the loading direction (end splitting). This work demonstrates the impact of compositional variation, tailored by additive manufacturing, on the mechanical performance of ceramic composites.

Investigating mechanical properties of 3D printed porous titanium scaffolds for bone tissue engineering

Objective. Three-dimensional (3D) printed porous titanium scaffolds serve as a bone tissue engineering technology that offers a promising solution for addressing bone defects. The scaffold’s pore structure offers structural support and facilitates the proliferation of bone cells. Therefore, investigating the aperture and pore shape is of crucial for the development of 3D printed porous titanium scaffolds. Methods. Ti6Al4V scaffolds with the specified structure were fabricated using selective laser melting (SLM) technology. The scaffolds comprised fifteen cylindrical models measuring 20 mm in diameter and 20 mm in height. These models featured five scaffold shapes: imitation diamond-60°, imitation diamond-90°, imitation diamond-120°, regular tetrahedron and regular hexahedron. Each of these structural shapes was characterized by three different aperture sizes (400 μm, 600 μm and 800 μm). The porosity and mechanical properties of Ti6Al4V scaffolds were examined. Results. The measured porosity of Ti6Al4V scaffolds varied between 56.50% and 95.28%. The porosity increased with the size of the aperture. The mechanical properties tests revealed that, for identical apertures, the compressive strength and torsional strength were influenced by the configuration of the unit structure. Furthermore, the positive and lateral compressive strength as well as torsional strength of various unit structures exhibited distinct advantages and disadvantages. Within a uniform unit structure shape, the compressive strength and torsional strength were found to be correlated with the size of apertures, indicating that larger apertures result in decreased compressive and torsional strength. Conclusion. The configuration of the aperture and the shape of the pore were identified as significant factors that influenced the compressive strength. The compressive strength of Ti6Al4V scaffolds with various unit structure shapes exhibited both advantages and disadvantages when subjected to positive, lateral, and torsional forces. The enlarged aperture augmented the scaffold’s porosity while diminishing its compressive and torsional strength.

Drug loading strategy of modular self‐assembly mode: Curcumin pyrimidine derivatives mediated by pH‐sensitive materials

AbstractChemotherapy drugs often cause various adverse reactions and affect normal tissues, so it is of great significance to design effective targeted anti‐tumor drug delivery methods. We constructed a series of self‐assembled supramolecular modular structures and explored whether they could become an effective targeted antitumor fluorescent agent. UV and fluorescence spectra show that it has fluorescence. The drug release curve was determined by dialysis method and the results showed that the release rate of PCB series composites was the highest under pH = 5. The curcumin pyrimidine derivative was embedded in the structure, and the formation of the complex was confirmed by infrared spectroscopy. The results for the cell imaging indicated that with the decrease of environmental pH value, the ability of PCB‐1 and PCB‐2 to penetrate the biofilm barrier into cells increased, suggesting that they have targeting action. The results of the cell viability test showed that PCB‐1 and PCB‐2 had a good inhibitory effect on MGC and HeLa cells. TEM showed that PCB‐1 was a regular hexahedron structure and PCB‐2 was a rod structure. In addition, the encapsulation efficiency of PCB‐1 and PCB‐2 was tested to be 86.50% and 88.57%, respectively, with drug loading rates of 27.62% and 28.38%, and Zeta potential values of +35 and +32. In conclusion, PCB‐1 and PCB‐2 are good potential anti‐tumor fluorescent agents.

Macroporous polymer-derived ceramics produced by standard and additive manufacturing methods: How the shaping technique can affect their high temperature thermal behavior

This work proposes the processing of porous ceramic lattices via three polymer-derived ceramic routes, namely powder bed fusion and infiltration, fused filament fabrication and replica, and a direct replica of a foamed polymer. A common feature in the processing of these lattices is the use of the same polysilazane as the preceramic source for the Si-C-N-O network that builds up during ceramization.We adopted rotated cube, honeycomb and randomized cellular geometries as a matter of comparison for thermal exchange when an air flow is forced through the structures up to 1050 °C. The three procedural pathways are discussed in their limitations regarding geometry, polymer-to-ceramic conversion, high-temperature heat exchange performance and durability. In this regard, while rotated cube geometry results in the best thermal exchange and highest pressure drop, we show a correlation between chemical composition and high temperature oxidation of the Si-C-N-O network, possibly attributed to the selection of the processing routes.

Temporal numerical analysis of beeswax PCM melting in a cube geometry subjected to a constant wall temperature condition

The ability of phase change materials (PCM) to store thermal energy has gained wide application area, like battery thermal management, solar water desalination and many other. The melting process of beeswax phase change material within the cube geometry with constant wall temperature (65 °C) boundary condition has been investigated using solidification and melting model. The fluid flow and heat transfer governing equations are solved using second order finite volume scheme. A PRESTO algorithm is applied for pressure-velocity coupling. The convergence criteria of 10−10 have been selected for energy equation, while 10−8 is selected for both momentum and continuity equations. The results like percentage variation along length-height and height-width plane for transient liquid fraction and temperature has been plotted, along with velocity streamlines within the cube geometry. From the obtained results it is concluded that the melting fraction and temperature of beeswax PCM is different in different planes and the major factors which affect the complete melting process is wall temperature, and the geometry. A difference of more than 0.1 °C in temperature has been recorded between mid-length-height and height-width plane while a difference of more than 2% in liquid fraction of PCM is observed. Even the uniformity of temperature and liquid fraction is notably influenced and vary along length, height, and width of cube geometry. Thus, it is concluded that melting process of PCM may affect the ability to store and release the heat energy which further affect the performance parameters of applied physical system.

Outsourcing Employee Recruitment And Selection Process

Outsourcing Employee Recruitment And Selection Process

Effects of FDM 3D printing parameters on PLA biomaterial components dimensional accuracy and surface quality

Since precise manufacturing is very important in different industries, the produced part surface quality and dimensional accuracy have been brought to attention in recent years. In this regard, in Fused Deposition Modeling (FDM) as a prototyping method, controlling the process parameters in order to customize the produced part has been a value-added ability which should be considered. Optimizing the process parameters helps to enhance the mentioned products’ properties. In this paper, influential process parameters, including print speed (PS), infill percentage (IP), and nozzle temperature (NT) were selected to examine. That was concluded NT increase from 195°C to 240°C, IP increase from 10% to 50% and PS decrease from 150 to 50 mm/min enhance dimensional accuracy including inner and outer ovality up to 30%, 53%, and 50%, respectively. PS is the most significant parameter on inner and outer ovality by 43.92% and 66.60% contribution, respectively. The density of the FDM part was affected mostly by the IP by 92.94% contribution which leads to the printed part density increment up to 13%. Other parameters have small effect on the density value. According to desirability method, that was resulted NT of 240°C, IP of 50%, and PS of 54 mm/min are the optimum parameters. Besides, verification tests were carried out and a maximum error of 7.5% was reported, which shows optimization confidence. In the following, part geometry influence on the final part surface roughness and dimensional accuracy was examined. The experiments demonstrated that cube geometry has the least surface roughness of 20 µm and dimensional error of 0.17 mm due to the independent motion of the axes. Also cone geometry has the highest dimensional error of 0.32 mm and surface roughness of 51 µm which was due to simultaneous axes motion and lateral face lower than 90°.

Ethnomathematics: Utilization and Introduction of Geometry Buildings Using Janur (Coconut Leaf)

One area of mathematics that requires a good understanding and depiction of abstract concepts is geometry. Therefore it is necessary to apply realistic learning. One type of realistic learning is ethnomathematics. Ethnomathematics is a bridge between mathematics and culture by linking culture and students' everyday experiences. Traditional crafts that can be lifted are creations from coconut leaves (janur) which can be formed into various kinds of craft creations that contain geometric shapes. The type of research used in this research is descriptive qualitative research. Data collection was used through literature and interviews. The results of the research show that creations from coconut leaves (janur) can be geometric shapes that can be used as ethnomathematics objects. These forms include (1) coins that can be made into hexagons, (2) kerises that have elements of equilateral triangles, right triangles, and parallelograms, (3) diamond bricks that have elements of square geometry lengths and blocks, (4) balls (balans) which have square and cube geometry elements, (5) sinta diamonds which have rhombus geometry elements and rhombus upright prisms. Other geometric elements contained in the janur creations are congruence, angles, and symmetry.
 Keywords: ethnomathematics, geometry, coconut leaves.

Evaluation of the Number of Degrees of Freedom of the Field Scattered by a 3D Geometry.

The solution to an ill-posed linear inverse problem requires the use of regularization methods to achieve a stable approximation solution. One powerful approach is the truncated singular value decomposition (TSVD), but it requires an appropriate choice of the truncation level. One suitable option is to take into account the number of degrees of freedom (NDF) of the scattered field, which is defined by the step-like behavior of the singular values of the relevant operator. Then, the NDF can be estimated as the number of singular values preceding the knee or the exponential decay. Therefore, an analytical estimation of the NDF is significant for obtaining a stable, regularized solution. This paper addresses the analytical estimation of the NDF of the field scattered by the surface of a cube geometry for a single frequency and the multi-view case in the far-zone. In addition, a method is proposed to find the minimum numbers of plane waves and their directions to achieve the total estimated NDF. The main results are that the NDF is related to the measure of the surface of the cube and can be achieved by only considering a limited number of impinging plane waves. The efficiency of the theoretical discussion is demonstrated through a reconstruction application for microwave tomography of a dielectric object. Numerical examples are provided to confirm the theoretical results.

One-pot synthesis of bimetallic CeCu-SAPO-34 for high-efficiency selective catalytic reduction of nitrogen oxides with NH3 at low temperature

NH3 selective catalytic reduction (SCR) has been widely recognized as a promising technique for reducing nitrogen oxides from diesel vehicle exhausts. High-efficiency SCR catalysts that could perform at low temperatures are essential to denitration. In this work, a series of bimetallic CeCu-SAPO-34 molecular sieves were synthesized by one-step hydrothermal method. The CeCu-SAPO-34 maintained good crystallinity and a regular hexahedron appearance of Cu-SAPO-34 after introducing Ce species, while exhibiting a higher specific surface area and pore volume. The as-prepared CeCu-SAPO-34 with 0.02% (mass) Ce constituent exhibited the best catalytic activity below 300 oC and a maximum NOx conversion of 99% was attained; the NOx removal rates of more than 68% and 94% were achieved at 150 °C and 200 °C, respectively. And the introduction of cerium species in Cu-SAPO-34 improves the low-temperature hydrothermal stability of the catalyst towards NH3-SCR reaction. Additionally, the introduced Ce species could enhance the formation of abundant weak Brønsted acid centers and promote the synergistic effect between CuO grains and isolated Cu2+ to enhance the redox cycle, which benefit the NH3-SCR reaction. This work provides a facile synthesis method of high-efficiency SCR denitration catalysts towards diesel vehicles exhaust treatment under low temperature.

Effects of ellipsoidal and regular hexahedral particles on the performance of the waste heat recovery equipment in a methanol reforming hydrogen production system

Hydrogen production from methanol has attracted attention due to its wide range of raw material sources and mature technology. Using waste heat of industrial high temperature solid particles like blast slag and steel slag etc. To provide vaporization heat and reaction heat for the reaction between methanol and water is an emerging technology for hydrogen production from methanol, which can save additional thermal energy resources. Herein, the performances of equipment that uses the waste heat of ellipsoidal and regular hexahedral particles to provide a heat source for methanol to hydrogen were explored by the DEM-CFD method. Compared with spherical particles of the same equivalent diameter, ellipsoidal and regular hexahedral particles have poor fluidity in the stagnant area, and the empty area is enlarged and irregular in shape. The average velocity peaks of the ellipsoidal and regular hexahedron particles are larger than those of spherical particles, and the overall mean velocity fluctuation of ellipsoidal particles is similar to that of spherical particles while the regular hexahedron particles' is larger. The average temperature drop rate of the ellipsoidal and regular hexahedral particles is slower than that of spherical particles, the uniformity of temperature distribution is worse than that of spherical particles. The ellipsoidal and regular hexahedral particles’ average effective heat transfer coefficient is smaller than that of spherical particles, and the heat transfer effect is weaker than that of spherical particles. The effective heat transfer coefficient of ellipsoidal particles is 2.95 W/(m−2∙K−1) lower than that of spherical particles and the effective heat transfer coefficient of hexahedral particles is 6.09 W/(m−2∙K−1) lower than that of spherical particles. Therefore, compared with the spherical particles of the same equivalent diameter, ellipsoidal and regular hexahedral particles produce less hydrogen.

Design and elaboration of various multilayer beam splitters

Three types of beam splitters: neutral, dichroic and polarizing are designed and elaborated on the base of multilayer interference coatings. The MacNeille’s cube geometry is applied. The software „TFCalc-3.5“ is used for matching the calculated with the measured spectra thus obtaining the optical constants of the vacuum deposited materials and the layer thickness. The technological parameters of the laboratory samples are established as a protocol for their manufacture.

Research on dynamic energy optimization strategy of park smart energy system with complementary multi-energy

The only way to develop a smart grid is to build a smart energy system in the park with coordinated optimization of source, network and load, and flexible interaction. In order to achieve the best operation of the multi-energy complementation of cooling, heating, and electricity in the smart energy system of the park when the output of renewable energy is uncertain, the Latin hyper square sampling method and the synchronous back generation method are used to analyze and model the uncertainty of renewable energy in the system. A model for the optimal operation of the integrated energy system for cooling, heating, and electricity is established. This model considers various demand response measures of controllable load and electric energy storage and considers how source, load, and storage can work together to reduce energy consumption. After conducting a multi-scenario simulation study, it is determined that this approach may significantly boost the park’s operational dependability and economic performance.

Simultaneous removal of sulfate and nitrate from real high-salt flue gas wastewater concentrate via a waste heat crystallization route

Flue gas wastewater concentrate was acidic and highly saline, and generated from the evaporator of desulfurization wastewater in power/heating plant. Its conventionally sprayed into flue gas pipeline and completely evaporated to generate hazardous halite into flue gas ash. Herein, a facile low-temperature thermal route was developed to treat the concentrate without the generation of any hazardous waste. The results showed that the concentrate was at pH 0.2 and contained 59 g/L sulfate, 13.1 g/L nitrate and 16.4 g/L chloride. When it was thermally treated at 150 °C (similar to the temperature of waste heat in power/heating plant), more than 99% sulfate and 97% nitrate were effectively removed with the addition of aluminum subacetate reagent. Without aluminum subacetate reagent, the removal of sulfate and nitrate only achieve by 2.8% and 9.1%. During the thermal treatment, the sulfate reacted with aluminum ion to form regular hexahedron natroalunite, whilst the nitrate was eliminated as nitrogen gas via the redox reaction between nitrate and organics (e.g., subacetate). The analysis of Gibbs free energy revealed that the formation of natroalunite took placed at the temperature > of 67 °C and accelerated at high temperature, but the reduction of nitrate was pH-dependent and accelerated at the initial pH < of 0.4. With the formation of natroalunite, the decrease of chloride from 16.4 g/L to 14.7 g/L were also observed, and the treated concentrate can be reused in the flue gas desulfurization triple-chambered process. In summary, this method showed merits to not only reuse the waste heat in power/heating plant for the effective removal of sulfate and nitrate from the flue gas wastewater concentrate, but also produce the recycled water and the value-added natroalunite particles.

Joint Inversion of 3D Gravity and Magnetic Data under Undulating Terrain Based on Combined Hexahedral Grid

As an effective underground imaging method, the joint inversion of the gravity and magnetic data has an important application in the comprehensive interpretation of mineral exploration, and unstructured modeling is the key to accurately solving its topographic problem. However, the traditional tetrahedral grid can only impose the gradient-based constraints approximately, owing to its poor arrangement regularity. To address the difficulty of applying a cross-gradient constraint in an unstructured grid, we propose a joint inversion based on a combined hexahedral grid, which regularly divides the shallow part into curved hexahedrons and the deep part into regular hexahedrons. Instead of a cross-gradient in the spatial sense, we construct a geometric sense “cross-gradient” for a structural constraint to reduce the influence of approximation. In addition, we further correct the traditional sensitivity-based weighting function according to element volume, to make it suitable for an unstructured grid. Model tests indicate that the new grid can impose the cross-gradient constraint more strongly, and the proposed correction can effectively solve the false anomaly caused by the element volume difference. Finally, we apply our method to the measured data from a mining area in Huzhong, Heilongjiang Province, China, and successfully invert out the specific location of a known skarn deposit, which further proves its practicability.

A Novel Design Method of Gradient Porous Structure for Stabilized and Lightweight Mandibular Prosthesis.

Compared to conventional prostheses with homogenous structures, a stress-optimized functionally gradient prosthesis will better adapt to the host bone due to its mechanical and biological advantages. Therefore, this study aimed to investigate the damage resistance of four regular lattice scaffolds and proposed a new gradient algorithm for stabilized and lightweight mandibular prostheses. Scaffolds with four configurations (regular hexahedron, regular octahedron, rhombic dodecahedron, and body-centered cubic) having different porosities underwent finite element analysis to select an optimal unit cell. Meanwhile, a homogenization algorithm was used to control the maximum stress and increase the porosity of the scaffold by adjusting the strut diameters, thereby avoiding fatigue failure and material wastage. Additionally, the effectiveness of the algorithm was verified by compression tests. The results showed that the load transmission capacity of the scaffold was strongly correlated with both configuration and porosity. Scaffolds with regular hexahedron unit cells can withstand stronger loads at the same porosity. The optimized gradient scaffold showed higher porosity and lower maximum stress than the target stress value, and the compression tests also confirmed the simulation results. A mandibular prosthesis was established using a regular hexahedron unit cell, and the strut diameters were gradually changed according to the proposed algorithm and the simulation results. Compared with the initial homogeneous prosthesis, the optimized gradient prosthesis reduced the maximum stress by 24.48% and increased the porosity by 6.82%, providing a better solution for mandibular reconstruction.

In situ quality monitoring in direct energy deposition process using co-axial process zone imaging and deep contrastive learning

Many strategic industrial sectors prefer Directed Energy Deposition (DED) to other Additive Manufacturing (AM) technologies due to the high material deposition and build rates. However, the inadvertent formation of defects such as porosity, micro-cracks and microstructure anomalies hinders its adoption in industries that require specific mechanical and microstructural properties. These defects are caused by undesirable fluctuations in process conditions such as material flow rate, laser power, melt pool dynamics, environment gas composition, temperature gradients. This research proposes in situ quality monitoring of DED using images of process zone and contrastive learning-based Convolutional Neural Network (CNN). Experiments included deposition of titanium powder (Cp-Ti, grade 1) with the particle size ranging between 45 and 106 μm on the base plate (99.6 % Ti6Al4V grade 1), forming a cube geometry. The process parameters were tuned to achieve six quality grades. The video of the process zone was recorded co-axially to the laser beam during the entire manufacturing, which was eventually used as the input to train CNN's based on contrastive losses. An in situ monitoring strategy for classifying the different quality grades was demonstrated in a supervised and semi-supervised manner, with an accuracy ranging between 89 % and 97 %. The performance of the developed framework was compared to an alternative clustering technique, namely t-distributed stochastic neighbour embedding, justifying the efficiency of our approach. The developed methodology demonstrates the possibility to track workpiece manufacturing quality using simple CCD cameras with minimum interventions on the commercial machines.

Security Enhancement in Coherent OFDM Optical Transmission With Chaotic Three-Dimensional Constellation Scrambling

In this paper, we propose and experimentally demonstrate a novel hybrid chaos-based three-dimensional (3-D) constellation scrambling scheme to simultaneously improve the physical layer security and transmission performance of the coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. A 3-D regular hexahedron signal constellation is constructed by the constellation figure of merit principle, which not only expands the encryption dimension but improves the error performance. The dynamic parameters for constellation scrambling are generated by the 5-D hybrid chaotic scheme based on the combination of a 3-D hyperchaotic Hénon mapping and two independent 1-D Logistic mappings, as such a key space of ∼10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">133</sup> is introduced to enhance the security level of OFDM data encryption during transmission. Furthermore, a transmission experiment for encryption of 144 Gbps 16-quadrature-amplitude-modulation OFDM data over a 100 km standard single-mode fiber in a CO-OFDM system is demonstrated. Compared with the case of using the 3-D rectangular constellation, a 2 dB bit error rate performance improvement is achieved. The results show that the proposed scheme could effectively enhance the system security and transmission performance, which suggests a scalable strategy for future physically secured CO-OFDM systems.

Erratum to “Topological structure of Rubik’s cube mechanism and synthesis of the regular hexahedron Rubik’s cube mechanism”

Erratum to “Topological structure of Rubik’s cube mechanism and synthesis of the regular hexahedron Rubik’s cube mechanism”