Center Of Unit Cell Research Articles

Experimental study on composite spherical-roof contoured-core (SRCC) sandwich panels under the V-shaped quasi-static indentation loading

The paper investigated the experimental study of composite spherical-roof contoured-core (SRCC) sandwich panels under a V-shaped quasi-static indentation (QSI) test. The carbon fiber, glass fiber, aramid fiber, hybrid carbon/aramid, and glass fiber chopped strand mat sheets were used to manufacture the composite cores, which used the hand layup and hot compression techniques. The polylactide (PLA) core was fabricated using fused deposition modelling (FDM). The V-shaped indenter had a 65° angle and was set at 1 mm/min as indentation speed in the experimental test. It was found that the maximum indentation deflection was 35.49 mm on the SRCC sandwich panel with a hybrid carbon/aramid core compared to other composite cores. Furthermore, it was localized fiber fracture, matrix damage, delamination, inwards fronds, and debonding damage mode on composite SRCC sandwich panels, which was visually shown at the central SRCC core unit cell. It is highlighted that aramid fiber and hybrid carbon/aramid materials can provide outstanding impact characteristics, which have great potential to be used as impact-resistant sandwich structures.

Cation Adaptive Structures Based on Manganese Cyanide Prussian Blue Analogues: Application of Powder Diffraction Data to Solve Complex, Unprecedented Stoichiometries and New Structure Types.

A Mn(II) salt and A+ CN- under anaerobic conditions react to form 2-D and 3-D extended structured compounds of Am MnII n (CN)m+2n stoichiometry. Here, the creation and characterization of this large family of compounds, for example AMnII 3 (CN)7 , A2 MnII 3 (CN)8 , A2 MnII 5 (CN)12 , A3 MnII 5 (CN)13 , and A2 MnII [MnII (CN)6 ], where A represents alkali and tetraalkylammonium cations, is reviewed. Cs2 MnII [MnII (CN)6 ] has the typical Prussian blue face centered cubic unit cell. However, the other alkali salts are monoclinic or rhombohedral. This is in accord with smaller alkali cation radii creating void space that is minimized by increasing the van der Waals stabilization energy by reducing ∠Mn-N≡C, which, strengthens the magnetic coupling and increases the magnetic ordering temperatures. This is attributed to the non-rigidity of the framework structure due the significant ionic character associated with the high-spin MnII sites. For larger tetraalkylammonium cations, the high-spin Mn sites lack sufficient electrostatic A+ ⋅⋅⋅NC stabilization and form unexpected 4- and 5-coordinated Mn sites within a flexible, extended framework around the cation; hence, the size, shape, and charge of the cation dictate the unprecedented stoichio-metry and unpredictable cation adaptive structures. Antiferromagnetic coupling between adjacent MnII sites leads to ferrimagnetic ordering, but in some cases antiferromagnetic coupling of ferrimagnetic layers are compensated and synthetic antiferromagnets are observed. The magnetic ordering temperatures for ferrimagnetic A2 MnII [MnII (CN)6 ] with both octahedral high- and low-spin MnII sites increase with decreasing ∠Mn-N≡C. The crystal structures for all of the extended structured materials were obtained by powder diffraction.

Superconductivity of Ta-Hf and Ta-Zr alloys: Potential alloys for use in superconducting devices

The electronic properties relevant to superconductivity are reported for bulk Ta-Hf and Ta-Zr body centered cubic alloys, in a large part to determine whether their properties are suitable for potential use in superconducting qbits. The body centered cubic unit cell sizes increase with increasing alloying. The results of magnetic susceptibility, electrical resistivity, and heat capacity characterization are reported. While elemental Ta is a type I superconductor, the alloys are type II strong coupling superconductors. Although decreasing the electron count per atom is expected to increase the density of electronic states at the Fermi level and thus the superconducting transition temperature (${T}_{c}$) in these systems, we find that this is not sufficient to explain the significant increases in the superconducting ${T}_{c}$'s observed.

Creating long-range entangled Majorana pairs: From spin- 12 twisted Kitaev to generalized XY chains

Entangling a pair of far-distant qubits in many-body systems has been a challenging task in quantum computing. A robust entanglement was predicted in the rainbow states and generating nonlocal Bell pairs protected by a mirror symmetry was recently proposed. We investigate a way to create entangled Majorana fermions in the spin-$\frac{1}{2}$ Kitaev chain with open boundary conditions. The spin-$\frac{1}{2}$ Kitaev chain, a one-dimensional version of the honeycomb lattice with bond-dependent Ising interactions, has a macroscopic degeneracy related to the zero modes containing nonlocal spin strings. We show that applying a pair pulse sequence on the central unit cell of the chain promotes long-distance spin correlations and maximal bipartite entanglement entropy. We extend this method to the generalized bond-dependent spin-$\frac{1}{2}$ chain by introducing another set of Majorana fermions and make a comparison to the entangled Bell pairs. The time to reach maximal bipartite entanglement entropy is shorter in the Kitaev chain as the zero modes do not participate in the entangled pairs. An application of our results to a recently proposed twisted Kitaev chain, ${\mathrm{CoNb}}_{2}{\mathrm{O}}_{6}$, is presented and future directions are also discussed.

Near-field focused planar transmitarray with low profile design for microwave power transmission

This paper proposes a near-field focused (NFF) planar transmitarray with low profile operating in the C-band. A frequency selective surface (FSS) unit cell with a profile of only 0.15λ is designed by combining generalised scattering theory with full-wave simulations. To achieve better focusing, the transmission phase of the central unit cell of the transmitarray is adjusted to 90°. The focusing relative bandwidth is 13.7% at a centre frequency of 5.8GHz, which enables a good focusing effect to be achieved. Meanwhile, this paper evaluates the microwave power received at the receiver when the proposed transmitarray used in MPT system. The measured results show that loading the proposed transmitarray can improve the received power up to 510%. Futhermore, in the range of 220-660mm from the transmitarray, the received power can be increased to more than 300%.

Completely Elastic Deformation of Hydrogenated Ta Thin Films

Nanostructured metal hydrides could play a key role in a hydrogen economy. The nanostructuring or confinement of these materials as, e.g., thin films significantly affects the structural and functional properties. For tantalum hydride, a versatile hydrogen sensing material, we show that the confinement of tantalum as a thin film extends the solubility limit by suppressing the phase transition observed in bulk upon hydrogenation. Different from bulk, the body centered cubic unit cell continuously deforms with unequal lattice constants and angles between lattice vectors. This deformation ensures that the volumetric expansion is realized in the out-of-plane direction, and surprisingly, completely elastic in nature. The first-order phase transition suppression combined with the continuous elastic deformation of the tantalum unit cell over an extraordinary wide solubility range ensures the superb performance of tantalum and its alloys as a hysteresis-free optical hydrogen sensing range over a hydrogen pressure/concentration range of over 7 orders of magnitude.

Effects of cholesterol on the structure and collapse of DPPC monolayers

Cholesterol induces faster collapse by compressed films of pulmonary surfactant. Because collapse prevents films from reaching the high surface pressures achieved in the alveolus, most therapeutic surfactants remove or omit cholesterol. The studies here determined the structural changes by which cholesterol causes faster collapse by films of dipalmitoyl phosphatidylcholine, used as a simple model for the functional alveolar film. Measurements of isobaric collapse, with surface pressure held constant at 52 mN/m, showed that cholesterol had little effect until the mol fraction of cholesterol, Xchol, exceeded 0.20. Structural measurements of grazing incidence X-ray diffraction at ambient laboratory temperatures and a surface pressure of 44 mN/m, just below the onset of collapse, showed that the major structural change in an ordered phase occurred at lower Xchol. A centered rectangular unit cell with tilted chains converted to an untilted hexagonal structure over the range of Xchol = 0.0–0.1. For Xchol = 0.1–0.4, the ordered structure was nearly invariant; the hexagonal unit cell persisted, and the spacing of the chains was essentially unchanged. That invariance strongly suggests that above Xchol = 0.1, cholesterol partitions into a disordered phase, which coexists with the ordered domains. The phase rule requires that for a binary film with coexisting phases, the stoichiometries of the ordered and disordered regions must remain constant. Added cholesterol must increase the area of the disordered phase at the expense of the ordered regions. X-ray scattering from dipalmitoyl phosphatidylcholine/cholesterol fit with that prediction. The data also show a progressive decrease in the size of crystalline domains. Our results suggest that cholesterol promotes adsorption not by altering the unit cell of the ordered phase but by decreasing both its total area and the size of individual crystallites.

Homogenized models of conduction-advection-radiation heat transfer in porous media

Upscaled models are derived from the periodic homogenization technique for conduction-convection-radiation problem in porous media for the case of an opaque solid and transparent fluid. Thermal radiation at the pore-scale level is first described through a differential view factor between elementary surfaces. Such heat transfer mode is coupled with the conduction-convection mechanisms by a radiative flux in the fluid phase and a jump of conductive fluxes at the solid/fluid interface. In the framework of the periodic homogenization procedure, a macroscopic model is built with upscaled effective coefficients. Both cases of closed and open pores are studied. In the second case the radiative transfer cannot be restricted to the central unit cell. The radiation at the macroscale only affects the effective conductivity. The validity of the approach is illustrated by some simple examples. The main objective of this work is to establish the macroscopic equation form of the conduction-convection-radiation problem and to understand how the radiation affects the macroscopic behavior.

Bending behavior of hybrid sandwich composite structures containing 3D printed PLA lattice cores and magnesium alloy face sheets

ABSTRACT In this study, the bending behavior of novel magnesium alloy facesheet and 3D-printed polylactic acid (PLA) lattice core sandwich panels with enhanced interface adhesion has been investigated by joint experiment and simulation method. A reliable numerical model for predicting three-point bending behavior of hybrid sandwich panels was developed and an explicit finite element analysis using ABAQUS/Explicit with a self-written VUMAT user subroutine was conducted. Meanwhile, hybrid sandwich panels were evaluated experimentally by three-point bending tests in order to validate the results obtained in the FEA. The comparison results have shown that the FEA predictions are consistent with the experimental tests. The bending resistance of the hybrid PLA core/Mg alloy composite sandwich panel is better than that of the integrated PLA sandwich panel. Among the four lattice geometries studied, namely body-centered cubic (BCC), BCC with gradient distribution of struts (BCCG), BCC with vertical struts connecting all nodes (BCCV), and face and body centered cubic unit cell with vertical struts (F2BCCZ), the sandwich structure with BCCV lattice cores has the better bending bearing capacity. The core configuration and core density have a coupling effect on the bending properties and failure modes of the hybrid sandwich panels.

Oxide layer characterization by XRD and Rietveld refinements in maraging steel 300 aged in steam atmosphere

Maraging steels are martensitic steels hardened by precipitation of intermetallic compounds in thermal aging, with good machining properties and high strength, fracture toughness and corrosion resistance, being used in aircraft parts and rocket motor-case, tooling applications and nuclear plants. During thermal aging in steam atmosphere a protective and corrosion resistant oxide layer is formed over the bulk. In this work, conventional Bragg-Brentano geometry was used to identify the phases formed in four specimens of maraging steel grade 300 with different surface finishes that were previously solution annealed twice at (950 ± 5) °C for 1 h, air-cooled, and submitted to oxidation process under positive pressure about 1.5 kPa of steam at (480 ± 5) °C for 6 h, followed by forced air-cooling. Diffraction patterns were measured employing CuKα radiation, ranging 20º < 2θ < 85º and the Rietveld method was used to better characterize the structures identified. Through Rietveld refinements it was possible to conclude that the layer formed during heat treatment process is constituted by a transition metallic phase with a quasi-cubic face centered unit cell, and an oxide layer that includes hematite, magnetite and a spinel structure type MFe2O4, where M could be an alloying element, for all analyzed samples.

Structure solution of incommensurately modulated La6MnSb15

Abstract La6MnSb15 is synthesized from the constituent elements in quartz ampoules at 973 K. Crucial for the quality of the obtained single-crystals was a slow cooling rate of 2 K h−1. The crystal structure of La6MnSb15 was investigated via single-crystal X-ray diffraction experiments, leading to the observation of superstructure reflections as described in the literature. Two crystals, with refined compositions of La6MnSb15 (1) and La6MnSb14.66(1) (2) were obtained from different batches, yet both showed an orthorhombic body centered unit cell as well as additional reflections at q 1 = (0,0,0.258(1)) for crystal (1) and q 1 = (0,0,0.244(1)) for crystal (2). The structure could be solved and refined in superspace group Immm(00γ)000 (71.1.12.1), leading to a concise structural model. Due to γ not being exactly 1/4, an incommensurate modulation is present in the presented compounds. In order to describe the structural influence of the modulation in 3D, different approximants were chosen and the differences compared. Additionally, the temperature dependence of the electrical resistivity was investigated, indicating a metallic behavior of the title compound. This result is in line with the retro-theoretical investigation in the literature that counts excess electrons when using the Zintl–Klemm–Busmann concept. 121Sb Mößbauer-spectroscopic investigations at 78 K show a broad signal with an average isomeric shift of δ ∼ −10 mm s−1, in line with a negatively charged Sb species. The massive line broadening can be explained by the large number of crystallographic antimony sites in the basic structure and the approximant.

Identifying and characterizing translationally modulated molecular crystal structures.

Most structural (i.e. displacive) modulations make molecules independent that had been related by translation in a phase having a smaller or centered unit cell. In the modulated structure the independent molecules are differentiated by small translations, rotations, and/or conformational changes but an approximate translational relationship is normally retained. A program has been written to identify such pseudotranslations because they can be difficult to find by eye and because they combine with each other and with lattice translations in ways that can be confusing. To characterize the pseudotranslations the program calculates their fractional translational, orientational, and conformational components as well as several quality indicators. While many pseudotranslations are obvious, others are borderline; setting tolerances for identifying a pseudotranslation proved difficult. Defaults were chosen to reproduce experience-based judgment but they can be varied in the program input. The program was run for organic and for metallo-organic structures with R ≤ 0.075 in the 2019 release of the Cambridge Structural Database. The frequency of pseudotranslations increases with Z' and is approximately 50% for Z' > 4. Some structures were found in which an identified pseudotranslation cannot correspond to a modulation. These include structures in which some but not all of the molecules are related by pseudotranslations and structures in which pseudotranslations in different parts of the unit cell have different directions.

Structural and electronic properties of the α-GeSe surface

We have investigated the structural and electronic properties of the α-GeSe surface using atomic force microscopy, scanning tunneling microscopy and density functional theory calculations. GeSe belongs to the group-VI transition metal monochalcogenides and occurs in two polymorphs, α-GeSe and β-GeSe. The most redundant polymorph, α-GeSe, has a structure that is very similar to black phosphorene. The α-GeSe surface has a centered rectangular unit cell with dimensions a = 3.8 Å and b = 4.4 Å, respectively. In scanning tunneling microscopy images only the Se atoms are resolved owing to the substantial transfer of electrons from the Ge to the Se surface atoms. This experimental finding is fully in line with density functional theory calculations. Scanning tunneling spectroscopy reveals that the α-GeSe surface is a p-type semiconductor with a band gap of 1.0 eV. The GeSe surface is stable at ambient conditions, which makes this material very appealing for technological applications.

Novel β-Ti35Zr28Nb alloy scaffolds manufactured using selective laser melting for bone implant applications

Titanium (Ti) based tissue engineering scaffolds can be used to repair damaged bone. However, successful orthopedic applications of these scaffolds rely on their ability to mimic the mechanical properties of trabecular bone. Selective laser melting (SLM) was used to manufacture scaffolds of a new β-Ti35Zr28Nb alloy for biomedical applications. Porosity values of the scaffolds were 83% for the FCCZ structure (face centered cubic unit cell with longitudinal struts) and 50% for the FBCCZ structure (face and body centered cubic unit cell with longitudinal struts). The scaffolds had an elastic modulus of ∼1 GPa and a plateau strength of 8–58 MPa, which fall within the values of trabecular bone (0.2–5 GPa for elastic modulus and 4–70 MPa for compressive strength). The SLM-manufactured β-Ti35Zr28Nb alloy showed good corrosion properties. MTS assay revealed that both the FCCZ and FBCCZ scaffolds had a cell viability similar to the control. SEM observation indicated that the osteoblast-like cells adhered, spread and grew healthily on the surface of both scaffolds after culture for 7, 14 and 28 d, demonstrating good biocompatibility. Overall, the SLM-manufactured Ti35Zr28Nb scaffolds possess promising potential as hard-tissue implant materials due to their appropriate mechanical properties, good corrosion behavior and biocompatibility. Statement of SignificanceNovel β Ti35Zr28Nb alloy scaffolds with FCCZ and FBCCZ structures were successfully fabricated by selective laser melting (SLM) for biomedical applications. The scaffolds showed values of elastic modulus of ∼1 GPa and plateau strength of 8–58 MPa, which fall within the ranges of the mechanical properties of trabecular bone. The SLM-manufactured β Ti35Zr28Nb alloy showed good corrosion properties. Both SLM-manufactured FCCZ and FBCCZ scaffolds exhibited good biocompatibility, with osteoblast-like cells attaching, growing, and spreading in a healthy way on their surfaces after culturing for different periods up to 28 d.

BH4 dissociation on various metal (1 1 1) surfaces: A DFT study

In this study, the catalytic effect of various metal surfaces on the sequential decomposition of BH4 molecule has been studied by Density Functional Theory (DFT) for the first time. For this purpose, the sequential dissociation of BHx (x = 0 → 4) molecules on Au, Cu, Al and Ag (1 1 1) surfaces were systematically investigated. At first, ground state structures of BHx (x = 0 → 4) molecules and their decomposed versions such as BHx + yH (x + y = 4) were obtained. Then, transition state search calculations were performed to find activation barriers related to every BHx + yH (x + y = 4) decomposition step until x = 0 has been reached. An additional hydrogen atom(s) remaining from a previous step accepted as if they(it) are(is) at infinite distances from the central unit cell of the surface because it is prerequisite to form energy diagram which keeps the number of the atom(s) constant. Our calculations were supported with the lateral interaction energies and the various bond distances to clarify catalytic abilities of the surfaces. It is concluded that Au(1 1 1) surface is the most active surface among the others however the activity of the Cu(1 1 1) surface can compete with it. Al(1 1 1) and Ag(1 1 1) surfaces are the least active surfaces. This knowledge can be used to develop strategies to design Cu-based cheap and active catalyst for hydrogen generation from borohydride dissociation.

Undulating the Lamellar Interface of Polymer–Surfactant Complex by Dendrimer

Self-assembly of the supramolecules formed by the complexation between poly(amidoamine) (PAMAM) generation four (G4) dendrimer and the surfactant, dodecylbenzenesulfonic acid (DBSA), generated a hexagonal columnar phase and a typical flat lamellar phase at low and high surfactant binding ratio, respectively, due to the dominance of the dendrimer to attain its natural curvature and the surfactant alkyl tails to reduce their hydrophobic interaction energy and packing frustration. Most strikingly, the delicate balance between these two free energy components at the intermediate binding ratios resulted in an undulated lamellar structure characterized by the centered rectangular unit cell. The finding demonstrates the power of dendrimer as a building block for expanding the morphological window of polymeric assemblies by modulating the interfacial curvature of microphase-separated structure.

Constructing Cost-Effective Crystal Structures with Table Tennis Balls and Tape That Allows Students To Assemble and Model Multiple Unit Cells

In this letter we present an innovative and cost-effective method of constructing crystal structures using Dual Lock fastening adhesive tape with table tennis (ping pong) balls. The use of these fasteners allows the balls to be easily assembled into layers to model various crystal structures and unit cells and then completely disassembled again. We have found that this method allows us to challenge the students in a hands-on activity where they construct the structures from single balls and not preconstructed layers. Furthermore, this method enables students to construct the body centered unit cell which is difficult to do with glue and table tennis balls.

The ash heap of crystallography: restoring forgotten basic knowledge

A critical analysis of some basic notions often overlooked in crystallographic education is presented to correct some common oversights occurring both in the literature and in textbooks. The crystal forms (face forms), defined in terms of their geometric eigensymmetry, are 47 in number, not 48 as often found in the literature. The split of the dihedron into dome and sphenoid calls for the consideration of the physical properties of the faces building a form; in that case, however, the same criterion should be used for all forms. By taking the handedness of the faces as representative of the physical properties of the faces, the occurrence of 130 crystallographic face forms (97 affine face forms and 33 enantiomorphic pairs) is demonstrated. Next, the correct use of non-coprime Miller indices when a centred unit cell is adopted is shown, and the inconsistent multiplication of Miller indices in the Bravais–Friedel–Donnay–Harker law is pointed out. A geometric derivation of the reflection conditions is reviewed. Finally, the inconsistent presentation of metric restrictions imposed by the structural symmetry is pointed out and corrected.

Eutectoid Flux Growth and Physical Properties of Single Crystal Ln117Ni54–ySn112–z (Ln = Gd–Dy)

Ln117Ni53–ySn112–z (Ln = Gd–Dy) have been grown via the eutectoid flux growth method, characterized using single crystal X-ray diffraction, and determined to have a face centered cubic unit cell with lattice parameters of a = 30.070(4), 29.862(5), and 29.823(4) A for the Gd, Dy, and Tb analogues. The compounds contain over 1100 atoms per unit cell with a complex bonding network and multiple magnetic sublattices. In addition, disorder is prevalent throughout the structure. These physical characteristics are ideal when searching for ultralow thermal conductivity materials. Magnetic susceptibility and electrical properties are presented, and all analogues exhibit positive Curie–Weiss constants, suggesting ferromagnetic interactions in each compound, in addition to a spin-glass component to the magnetic behavior.

Frequency distribution of the reduced unit cells of centred lattices from the Protein Data Bank

In crystallography, a centred conventional lattice unit cell has its corresponding reduced primitive unit cell. This study presents the frequency distribution of the reduced unit cells of all centred lattice entries of the Protein Data Bank (as of 23 August 2011) in four unit-cell-dimension-based groups and seven interaxial-angle-based subgroups. This frequency distribution is an added layer of support during space-group assignment in new crystals. In addition, some interesting patterns of distribution are discussed as well as how some reduced unit cells could be wrongly accepted as primitive lattices in a different crystal system.