Tetrahedral Shape Research Articles

Elucidating the natural–synthetic mismatch of Pb2+Te4+O3: The redefinition of fairbankite to Pb122+(Te4+O3)11(SO4)

AbstractFor four decades fairbankite was reported to have the formula Pb2+(Te4+O3), but repeated attempts to isolate fairbankite crystals for structural determination found only the visually similar cerussite and, more rarely, anglesite. The crystal-structure determination of fairbankite using single-crystal X-ray diffraction, supported by electron microprobe analysis and X-ray powder diffraction on the type specimen, has shown that fairbankite contains essential S, along with Pb, Te, and O. The chemical formula of fairbankite has been revised to Pb122+(Te4+O3)11(SO4). This change has been accepted by the IMA–CNMNC, Proposal 19-I. The crystal structure of fairbankite [space group P1 (no. 1); revised cell: a = 7.0205(3) Å, b = 10.6828(6) Å, c = 14.4916(8) Å, a = 75.161(5)°, b = 81.571(4)°, g = 83.744(4)°, V = 1036.35(9) Å3, and Z = 1] is the first atomic arrangement known to contain a Te34+O96− non-cyclic, finite building unit. Fairbankite has an average structure, formed from a 3D framework of Pb2+On polyhedra, Te4+On polyhedra, and SO4 tetrahedra in a 12:11:1 ratio. The stereoactive lone pairs of the Pb2+ and Te4+ cations are oriented into void space within the structure. Fairbankite contains two mixed sites statistically occupied by Te4+ and S6+ in approximately 4:1 and 1:4 ratios. These two sites possess Te4+ in trigonal-pyramidal environment and S6+ in tetrahedral environment (with an additional O site to create tetrahedral SO4 shape for the S-dominant site). Six of the 10 fully occupied Te4+ sites have Te4+ in trigonal-pyramidal environment, while four have Te4+ at the center of highly distorted Te4+O4 disphenoids. The disphenoids allow for the creation of two dimeric Te24+O64− units in addition to the Te34+O96− trimeric unit, which contains two disphenoids. All linkage between disphenoids and trigonal pyramids is via corner-linking. Secondary connectivity is via long Te–O and Pb–O bonds.

Shape-Controlled HgTe Colloidal Quantum Dots and Reduced Spin-Orbit Splitting in the Tetrahedral Shape.

Spherical and tetrahedral HgTe colloidal quantum dots (CQDs) are synthesized, and their doping is tuned electrochemically. Compared to spherical dots of a similar volume, the tetrahedral CQDs show a decrease in confinement energy as well as a sharper band edge absorption. The intraband spectra of the tetrahedral CQDs also display a smaller splitting from spin-orbit coupling. The shape-controlled synthesis with an improved size distribution and sharper optical features could find applications in optoelectronic devices.

A deformable tetrahedron rolling mechanism (DTRM) based on URU branch

The purpose of this paper is to put forward a novel deformable tetrahedron rolling mechanism (DTRM). This new reconfigurable mobile mechanism with the external tetrahedral shape can be regarded as a parallel mechanism with a variable platform, that is constructed by four vertices and six edges corresponding to four platforms and six URU chains. Mechanical design is introduced, and the degree of freedom (DOF) is analyzed. Equivalent planar mechanism analysis method is proposed for the symmetrical mechanical structure to simplify the theoretical analysis process. Based on the symmetric-drive rolling locomotion, impact and non-impact rolling gait are planned, respectively corresponding to different joints workspace, to reduce the displacement error. Aiming at non-impact rolling gait, the motion strategy is established instead of moving with pre-set driving parameters, as the basis of the control system. Then a trajectory optimization of the center of mass (CM) based on actuator torque analysis is carried out to reduce the actuator torque. To verify the rolling locomotion, we present the results of a series of experiments, performed on a manufactured prototype.

Determination of Chemical Composition of Compounds in Lead-Free Solder Alloy Sn-Zn-Al Using SEM/EDS

Energy-dispersive spectroscopy (EDS) has been an important technique to determine the chemical composition of an alloys and compounds. However, there are several considerations that should be taken into account to get reliable chemical analysis. The relation between electron–matter volume and acceleration voltage are the most important parameter. In this work, chemical composition of diamond-like phases (DLP) presented in Sn-Zn-Al solder alloys was analyzed. Using focused ion beam, a tetrahedral shape of the DLP was elucidated. Monte Carlo simulations and experimental analyses were used to investigate the effect of acceleration voltages on chemical composition. It was found that at an acceleration voltage of 10 kV, the energy required for exciting the characteristic x-ray was enough for a reliable determination of the DLP composition. Besides, it was found that the electron–matter interaction volume was inside the DLP and the matrix contribution was reduced, giving a chemical composition rather close to the real.

Origin of Life’s Chirality

The phase transition at 72K in ice XIc accommodating water molecules’ irregular tetrahedral shape I discovered in 1967 restores the confidence in science measuring c challenged. Forming in polar pools of N2 during a primordial ice-age, fluctuating temperatures released latent energy as λ ~4µ laser light. Multiple reflection polarized it and deoxynucleotides on tropical water surfaces were polymerized, creating chiral DNA, uniquely explaining life’s origin. 
 ‘Transport DNAs’ sharing tRNA’s H-bond-lined pores concentrated life’s ingredients in coacervates. Replicate tDNAs originated life. DNA’s stability makes it life’s likely precursor. ‘Differentiation DNAs’ selecting tDNAs control cell diet and tissue specialization. Nine pathways deploying trace elements as carriers control metabolism. Mutant tDNAs and dietary deficits account for morbidity.
 ‘Minion’ DNA/oligopeptide complexes optimize chromosomes replication. They function as biological clocks, chips-in-the-brain and nuclear fusion reactors. Minion logic reinterprets 20th century scientific axioms. Resonant cavities coupling chemical to mechanical energy efficiently.

Molecular structures and thermodynamics of stable N4, N6 and N8 neutral poly-nitrogens according to data of QCISD(T)/TZVP method

By means of the QCISD(T)/TZVP and G4 quantum-chemical calculation methods, the possibility of the existence of nitrogen molecules having the composition N4, N6, N8 and N10, has been discussed. On the basis of the data obtained, existence of four types of neutral poly-nitrogens with number of atoms from 4 to 8, namely N4 with rectangular and regular tetrahedron shapes, N6 in a form remotely resembling an “open book”, and N8 in a form of cube, has been shown. The values of geometric parameters of molecular structures in each of these compounds have been presented. Also, the key thermodynamic parameters of formation (enthalpy ΔfH0, entropy Sf0, Gibbs’ energy ΔfG0) of these compounds have been calculated. Using this data, the enthalpies and entropies of processes of oxidation of these compounds with molecular oxygen (O2) have been found; it has been noted that all these reactions are exothermic. Based on this fact, it has been concluded that the given neutral poly-nitrogens may be used as combustible materials.

3D printing of tuneable agglomerates: Strain distribution and effect of internal flaws

The current study presents a novel and reliable method for producing 3D printed agglomerates with different colour distributions and material properties with 2-fold aims: providing feasible and accurate control on compression of agglomerates under different compression angles, and better tracking of individual particle position after agglomerate breakage. Multi-coloured agglomerates in cubic tetrahedral and random sphere shapes were printed with both rigid and soft bonds. The printed agglomerates were analysed thoroughly of their surface and structural properties including surface roughness and printing accuracy. The agglomerate breakage behaviours under static compression were analysed as a function of bond strength, loading rate and loading directions, with strain distribution plotted over the random sphere agglomerate structure. In addition, agglomerate structures with designed internal macro-voids in different positions and sizes were also created for breakage study, in an effort to better understand parameters governing the mechanical properties of agglomerates with cavities and voids which is inevitable in particle industry but poorly understood at present.

Novel modifications of elemental nitrogen and their molecular structures – a quantumchemical calculation

Using the quantum-chemical calculation methods QCISD and G3, the possibility of the existence of nitrogen molecules with the composition N4, N6, N8 and N10 has been discussed. On the basis of the data obtained, the conclusion about possibility of existence of three novel polymorphic modifications of elemental nitrogen with an even number of atoms in molecules, namely N4 with rectangular and regular tetrahedron shapes, and N6 in a form remotely resembling an open book, has been made. The values of bond lengths, valence and torsion angles, and oscillations frequencies in each of the above-mentioned forms of elemental nitrogen have been presented.

Synthesis and characterization of hexagonal and tetrahedral nanocrystalline Sb2O3 thin films prepared by chemical spray pyrolysis technique

Abstract Nanocrystalline hexagonal and tetrahedral shape Sb2O3 thin films of different concentrations have been successfully deposited onto glass substrates using chemical spray pyrolysis technique for the first time. The structural, morphological and compositional studies were carried out using X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM) and energy dispersive X-ray analysis (EDAX) respectively. The structural studies revealed that, deposited Sb2O3 thin films have polycrystalline nature having cubic senarmontite structure. The morphological and compositional studies revealed that deposited materials have hexagonal and tetrahedral shape which showing excellent agreement with theoretical composition. The optical characterization shows that deposited Sb2O3 exhibited direct band gap which varied from 3.43 to 3.71 eV depending upon the concentration of spray solution. Electrical resistivity of the Sb2O3 thin film decreases with an increase in temperature indicating the semiconducting nature. The activation energy of the film is found to be varying from 0.764 to 0.798 eV depending upon the concentration of spray solution.

Unraveling the atomic structure, ripening behavior, and electronic structure of supported Au20 clusters.

The free-standing Au20 cluster has a unique tetrahedral shape and a large HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gap of around 1.8 electron volts. The "magic" Au20 has been intensively used as a model system for understanding the catalytic and optical properties of gold nanoclusters. However, direct real-space ground-state characterization at the atomic scale is still lacking, and obtaining fundamental information about the corresponding structural, electronic, and dynamical properties, is challenging. Here, using cluster-beam deposition and low-temperature scanning tunneling microscopy, atom-resolved topographic images and electronic spectra of supported Au20 clusters are obtained. We demonstrate that individual size-selected Au20 on ultrathin NaCl films maintains its pyramidal structure and large HOMO-LUMO gap. At higher cluster coverages, we find sintering of the clusters via Smoluchowski ripening to Au20n agglomerates. The evolution of the electron density of states deduced from the spectra reveals gap reduction with increasing agglomerate size.

On the density of shapes in three-dimensional affine subdivision

The affine subdivision of a simplex $\Delta$ is a certain collection of $(n+1)!$ smaller $n$-simplices whose union is $\Delta$. Barycentric subdivision is a well know example of affine subdivision(see). Richard Schwartz(2003) proved that the infinite process of iterated barycentric subdivision on a tetrahedron produces a dense set of shapes of smaller tetrahedra. We prove that the infinite iteration of several kinds of affine subdivision on a tetrahedron produce dense sets of shapes of smaller tetrahedra, respectively.

A simulation study of the low temperature phase diagram of the methane monolayer on graphite: a test of potential energy functions.

We have used molecular simulation with two intermolecular potential models, TraPPE-UA and TraPPE-EH, the latter of which accounts for the tetrahedral shape, to study the effects of shape on methane adsorption on graphite. Both models give good descriptions of the vapour-liquid equilibria in the bulk phase, but adsorption on graphite is better described by the TraPPE-EH model. Molecular configurations in the monolayer, show the variation with temperature of the registry sites for the carbon and hydrogen atoms of the methane molecules. At temperatures below 70 K, the centre of mass (COM) of the molecules is in registry with the centre of the carbon hexagons. For temperatures above 70 K, a commensurate monolayer is initially formed as at low temperatures, then as the loading is increased the first layer remains in registry, but the COM of the methane molecules in the first layer shifts to the top of the graphite carbon atoms with the C-H bond pointing to carbon atoms in the second shell of a C-hexagon. At temperatures above 93 K, the first adsorbate layer goes through these two commensurate states and then undergoes a transition to an incommensurate solid. Finally, for temperatures greater than 110 K methane behaves like a pseudo spherical molecule.

Equilibrium synthesis and magnetic properties of BaFe12O19/NiFe2O4 nanocomposite prepared by co precipitation method

The hard and soft magnetic nanocomposites (BaFe12O19/NiFe2O4) at the ratio 1:1 were prepared by simple mixing and heat treatment. XRD peak indicates the formation of good crystalline quality of the prepared sample. The FTIR spectra reveals the bands for metal oxygen stretching which ranges from 584 cm−1 to 540 cm−1 forms the tetrahedral shape in nature. However, the hexaferrite site ranges from 580 cm−1 to 440 cm−1 and this bands assign to Ba-O and Fe-O bonds respectively. Furthermore, the UV–visible range, the observed absorption peak indicates that the prepared sample color is congo red, the characteristic absorption peaks at ~739 nm for BaFe12O19, 698 nm for NiFe2O4 and 780 nm for BaFe12O19/NiFe2O4. Overall, the ferrite powder seems agglomerated, but the microstructure shows its respective structure. The particle size of BaFe12O19 (hexagonal) is 150 nm, again the particle size of NiFe2O4 (cubic) is 89 nm apparently. Finally, the structure of composite (BaFe12O19/NiFe2O4) material seems to achieve intermediate and its particle size is 120 nm correspondingly.

Facet effect of Pt nanocrystals on catalytical properties toward glycerol oxidation reaction

Using nanocrystals with specific crystal facets is an effective way to enhance activity and selectivity for numerous catalytic reactions. However, the intrinsic facet effect is not fully understood. Herein, using Pt catalyzed glycerol oxidation reaction as the model system, the intrinsic facet effect on catalytic property is evaluated by three kinds of Pt nanocrystal catalysts with cubic, spherical and tetrahedral shapes. Size effect, support effect, surfactant effect as well as the metal-support interaction of the catalysts are avoided to the maximum extent. The supported Pt nanocubes enclosed by Pt(1 0 0) facets are found to exhibit much higher catalytic activity and stability for the aerobic oxidation of glycerol than catalysts with Pt nanotetrahedrons enclosed by Pt(1 1 1) facets. DFT calculations indicate that the adsorption of oxygen and glycerol would materialize easier on Pt(1 0 0) than on Pt(1 1 1). Furthermore, Pt(1 0 0) may prevent deactivation caused by product adsorption as well.

Synthesis of gold nanoparticles using Crinum macowanii bulb extracts and the application of these materials in blood detections at crime scenes.

We here in report the synthesis of gold nanoparticles (AuNPs) using a Crinum macowanii bulb water extract. The as-synthesized AuNPs were characterized using ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and a zeta potential-sizer. The results showed that the as-synthesized AuNPs were crystalline and mostly spherical in shape with a small mixture of triangular, tetrahedral, hexagonal, octagonal, and diamond shapes. The as-synthesized AuNPs together with those synthesized by conventional methods were subsequently used as enhancers for the luminol signal in blood detection. It was noted that the AuNPs synthesized from the Crinum macowanii bulb water extract could enhance the chemiluminescence signal for blood detection by luminol to the same extent as AuNPs prepared by conventional methods. Furthermore, both types of AuNPs served as fluorescence enhancers for blood detection when luminol was replaced with the bulb water extract.

Comparing the void space and long-range structure of an ionic liquid with a neutral mixture of similar sized molecules

We study the void space and the structure of a coarse-grained molecular model of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [C4mim][PF6] and the corresponding model of an uncharged liquid consisting of the same molecules but with zero charges as a function of temperature between 300 K and 600 K using molecular dynamics simulations. Long-distance radial correlation functions for representative sites and for interstitial spheres were calculated for the individual subsystems representing anions and cations. The geometry of the local structural arrangements was investigated using the technique of Delaunay simplices. As expected, the ionic liquid demonstrates a noticeable regularity with respect to the alternation of anions and cations, which is present in all studied distance-ranges. The structure of uncharged subsystems, however, demonstrates features typical for simple liquids, which are governed by geometrical laws of the dense disordered packing of impenetrable particles. A prominent structural feature of the studied ionic liquid is that the “mutually closest fours” of anions form configurations of pronounced tetrahedral shape with a cation being located in between them. Correspondingly, the cations (here represented by the position of their central site) also form tetrahedral configurations around an anion. In the uncharged system, such mutual arrangements are found to be absent. The analysis of the models for different temperatures demonstrates that the principal differences between the structures of the charged and uncharged subsystems remain present up to 600 K. Quite interestingly, the distribution of void spaces, as represented by the radii of interstitial spheres, is found to be consistently, albeit slightly broader for the charged model liquid.

Gram-Scale Synthesis of Tetrahedrite Nanoparticles and Their Thermoelectric Properties.

Here, we report a method for facile gram-scale synthesis of tetrahedrite (Cu12Sb4S13) nanoparticles (NPs) with high quality and good reproducibility. The obtained NPs had a well-defined tetrahedral shape with a mean edge length of ∼70 nm. We sintered the NPs by the hot press technique to fabricate a nanostructured pellet for thermoelectric measurements. The figure of merit (ZT) value of the pellet was 0.52 at 675 K, which was comparable with the ZT value of the non-nanostructured counterpart.

The inventory and spore morphology of ferns from Bengkalis Island, Riau Province, Indonesia

Abstract. Sofiyanti N, Isda MN, Juliantari E, Pranata S, Suriatno R. 2019. The inventory and spore morphology of ferns from Bengkalis Island, Riau Province, Indonesia. Biodiversitas 20: 3223-3236. Bengkalis Island is one of main islands at coastal region of Riau Province, Indonesia. The first fern inventory had been conducted on this island, to identify the fern checklist as well as examined the morphology of their spores. Samples were collected from 2 subdistricts and 12 study sites, using exploration method. The spore specimens were coated using AU, before observation using Scanning Electron Microscopy (SEM). A total of 22 fern species are recorded from Bengkalis Islands. These species belong to 3 orders, i.e. Gleicheniales (1 species), Polypodiales (20 species) and Schizaeales (1 species). The spore characteristic indicated similar unity of spore, i.e. monad spore, with triangular, subtriangular, tetrahedral and reniform shape. Three basic types of spore have been observed, i.e. monolete, dilete, and trilete. The spore class observed in this study are small (22 ± 0.88 µm), medium (27.35 ± 1.45 to 47.85 ± 0.88 µm) and large (51.34 ± 1.83 to 53.8 ± 1.81 µm). The ornamentation of perisphore is the main character to distinguished species within one genus.

A curvature operator for a regular tetrahedron shape in LQG

An alternative approach introducing a 3-dimensional (3D) Ricci scalar curvature quantum operator given in terms of volume and area as well as new edge length operators is proposed. An example of monochromatic 4-valent node intertwiner state (equilateral tetrahedra) is studied and the scalar curvature measure for a regular tetrahedron shape is constructed. It is shown that all regular tetrahedron states are in the negative scalar curvature regime and for the semi-classical limit the spectrum is very close to the Euclidean regime.

Precision enhancement in source localization using a double-module, three-dimensional acoustic intensity probe

The three-dimensional (3D) acoustic intensity probe is not popularly used for the source localization of acoustic source because of the large error even though the technique has been well known. In particular, the measured direction-of-arrival strongly depends on the frequency, which is a detrimental drawback that hampers the use of this method. Such spectral bias error, due to the discrete positioning and spacing of sensors surrounding the acoustic center, fluctuates in a nearly regular spectral pattern when a 3D acoustic intensity probe configured in a tetrahedral shape is used. In this work, two error compensation methods are tried: The first method is to adopt a double-module configuration, which is formed by the connected assembly of two intensity modules, but with different locations of acoustic centers for a spatial averaging effect. The second one is the 1/3-octave band averaging of the measured intensity spectrum within the effective measurement range. Because two probe modules are attached, they concatenate 1–3 sensors in the overlap position. Four double-module probes different in assembly configuration of involved two single-modules are tested: modules having a same acoustic center but twisted by 60°, inverted modules sharing one microphone and twisted by 60°, symmetric modules having the joint angle of 60° in the sharing edge, symmetric modules to a common face thus sharing three microphones. Measurements are conducted in an anechoic chamber by changing the source positions for 4 azimuth and 3 elevation angles. The results reveal that the maximum mean bias error of about 4° can be obtained by the double-module 3D acoustic intensity method, depending on the module configuration and angular source position. This contrasts to the fluctuating direction-of-arrival within about ±10° error range, which is obtained by each single-module in a concatenated double-module. In particular, when the band averaging technique is applied to the measured data by the probe module composed of the inverted single modules, the maximum bias error can be reduced to less than 1° in both azimuth and elevation angles.