Unit Cell Dimensions Research Articles

Atomic-scale imaging of polyvinyl alcohol crystallinity using electron ptychography

Polyvinyl alcohol (PVA) is considered to have great potential in medical, pharmaceutical, and packaging applications because of its outstanding biocompatibility, water solubility, low density and relatively low cost. PVA crystallinity, central to the materials properties, has been studied by X-ray diffraction, but two possible crystal structures are mooted. Electron microscopic techniques can potentially image PVA at high resolution. Still, it is challenging for conventional electron microscopies because of the relatively low crystallinity of PVA, its severe beam sensitivity, and the poor contrast of light elements. Electron ptychography makes use of a 4D STEM dataset comprising the intensity in the STEM detector plane recorded as a function of each probe position and has lower sample damage and better phase-contrast compared to traditional techniques. Here, we use electron ptychography to image PVA crystallinity. The reconstructed images, which show good agreement in the unit cell dimension with X-ray diffraction data, can show how the atoms order in the materials, however, deviations from previous models derived from X-ray diffraction are observed. To interpret the data, we propose a series of changes based on previous models to formulate a description of PVA crystal structure. Simulated results from this new model accord well with the experimental images. This study manages to image both carbon and oxygen atoms in PVA, which has not previously been achieved by any conventional method. The results are expected to bring a new and deeper understanding of PVA crystal structure, and illustrate the opportunity presented by this approach for directly imaging molecular order in polymer crystals.

Structure of the Hexadecane Rotator Phase: Combination of X-ray Spectra and Molecular Dynamics Simulation.

Rotator phases are rotationally disordered plastic crystals, some of which can form upon freezing of alkane at alkane-water interfaces. Existing X-ray diffraction studies show only partial unit cell information for rotator phases of some alkanes. This includes the rotator phase of n-hexadecane, which is a transient metastable phase in pure alkane systems, but shows remarkable stability at interfaces when mediated by a surfactant. Here, we combine synchrotron X-ray diffraction data and molecular dynamics (MD) simulations, reporting clear evidence of the face-centered orthorhombic RI rotator phase from spectra for two hexadecane emulsions, one stabilized by Brij C10 and another by Tween 40 surfactants. MD simulations of pure hexadecane use the recently developed Williams 7B force field, which is capable of reproducing crystal-to-rotator phase transitions, and it also predicts the crystal structure of the RI phase. Full unit cell information is obtained by combining unit cell dimensions from synchrotron data and molecular orientations from MD simulations. A unit cell model of the RI phase is produced in the crystallographic information file (CIF) format, with each molecule represented by a superposition of four rotational positions, each with 25% occupancy. Powder diffraction spectra computed using this model are in good agreement with the experimental spectra.

Structural Investigation of Tetra-n-Butylammonium Perchlorate

The crystal structure of tetra-n-butylammonium perchlorate has been successfully elucidated using single-crystal X-ray diffraction. The compound crystallizes in the triclinic space group P1¯ with unit cell of dimensions a = 14.2706(7) Å, b = 20.6904(9) Å, c = 39.970(2) Å, α = 89.316(4)°, β = 88.638(4)°, and γ = 87.801(4)°. Although complicated by partial disorder, the structure has remarkable features where columns of some of the perchlorate anions running down [100] lie within what can be regarded as nanotubular entities formed by some of the tetrabutylammonium cations, while the remaining tetrabutylammonium cations lie in parallel columns surrounded by the remaining perchlorate anions, one entity being essentially the inverse of the other. Interactions within the structure have been characterized using Hirshfeld surface analysis and comparisons drawn with other unsolvated salts of the cation.

Role of Cu-substitution on microstructural, magnetic, magnetostrictive and dielectric properties of sintered NiFe2O4

This study examines the impact of Cu-amalgamation on the microstructural, magnetic, magnetostrictive, and dielectric properties of sintered nickel ferrite (NiFe2O4) ceramics. Without post synthesis calcination, the series of Ni1-xCuxFe2O4 (0 ≤ x ≤ 1) samples were synthesized via an autocombustion process with glycine (1 Mole/mole of metal ion) as a fuel. XRD analysis of the as-synthesized samples revealed that compositions up to x = 0.75 were phase pure. However, impurity CuFeO2 was detected in the x = 1 (CuFe2O4) sample, leading to its exclusion from further processing and testing. After sintering the compacted pellets (12 mm diameter and 3 mm thickness) at 1200 °C for 2 h, compositions up to x = 0.5 were confirmed as phase pure, prompting further characterization of these samples' structural, microstructural, magnetic, and dielectric properties. The unit cell dimension increased from 8.3268 Å for NiFe2O4 (x = 0) to 8.3560 Å for Ni0.5Cu0.5Fe2O4 (x = 0.50) due to the substitution of larger-sized ion (Cu2+) for the smaller-sized ion (Ni2+) in NiFe2O4. Notably, the addition of Cu facilitated substantial grain growth, as observed in the SEM micrographs, where the grain size increased from 556 nm for x = 0 to 13 μm for x = 0.5. As the Cu-content increased in Ni1-xCuxFe2O4, magnetic parameters such as TC (Curie temperature), K1 (Magnetocrystalline anisotropy constant), HC (Coercivity), and MS (Saturation magnetization) decreased. This decrease can be attributed to the replacement of the high-magnetic cation (Ni2+, 2 μB) with the low-magnetic cation (Cu2+, 1 μB) in the octahedral coordination site of NiFe2O4. The x = 0 and 0.5 samples exhibited a maximum magnetostriction strain (λmax) of ∽-35 ppm, and for x = 0.25 sample the value is −24 ppm. In terms of dielectric properties, the permittivity count of the x = 0 sample was higher than that of x = 0.25 and 0.5 samples in the lower frequency regime, likely due to a larger surface area (smaller grain size) contributing to significant surface polarization. Conversely, in the higher frequency regime, the samples with x = 0.25 and 0.5 demonstrated higher permittivity than the parent sample. The changes in dielectric behavior in the Cu-substituted samples were explained based on the microstructure of the samples.

Compact Sub‐Semicircular Axial Gradient Index Lens Synthesized by Metasurfaces: A Promising Solution for Miniaturized Antenna and Subwavelength Focusing Systems

AbstractWe present the design, fabrication, and experimental measurements of an Axial Gradient‐index (AGRIN) flat lens synthesized by 2D periodic metallic patches on a grounded dielectric slab, known as metasurfaces. Metasurfaces can be considered as artificial materials that possess unique characteristics, which mainly revolve around the two‐dimensional distribution of the structure. By manipulating the phase and amplitude of the near‐fields over the surface of the metasurface, specific values of the effective permittivity and permeability can be achieved, thereby regulating the overall field behavior by gaining control of the refractive index that is related to the aforementioned two material parameters. By configuring the refractive index, metasurfaces enable the manipulation of the direction in which electromagnetic waves propagate, as dictated by Snell's law. By varying the geometric dimensions of unit cells in each segment that compose the lens, the gradient refractive index profile required for our AGRIN lens can be achieved. A primary feature of this lens lies with its semicircular structure, in contrast to conventional circular ones. Its perimeter comprises a convex boundary and a straight one. In comparison to traditional circular lenses like the Luneburg lens and Maxwell fisheye lens, our proposed AGRIN lens offers the advantage of being more compact. Despite its smaller area, the AGRIN lens maintains its focusing ability. The AGRIN lens is capable of focusing over 71.75% of the energy from the incident wave onto the focal point. This efficient focusing ability, combined with its reduced size, makes the AGRIN lens highly advantageous for various applications.

Disordered Crystal Structure and Anomalously High Solubility of Radium Carbonate.

Radium-226 carbonate was synthesized from radium-barium sulfate (226Ra0.76Ba0.24SO4) at room temperature and characterized by X-ray powder diffraction (XRPD) and extended X-ray absorption fine structure (EXAFS) techniques. XRPD revealed that fractional crystallization occurred and that two phases were formed─the major Ra-rich phase, Ra(Ba)CO3, and a minor Ba-rich phase, Ba(Ra)CO3, crystallizing in the orthorhombic space group Pnma (no. 62) that is isostructural with witherite (BaCO3) but with slightly larger unit cell dimensions. Direct-space ab initio modeling shows that the carbonate oxygens in the major Ra(Ba)CO3 phase are highly disordered. The solubility of the synthesized major Ra(Ba)CO3 phase was studied from under- and oversaturation at 25.1 °C as a function of ionic strength using NaCl as the supporting electrolyte. It was found that the decimal logarithm of the solubility product of Ra(Ba)CO3 at zero ionic strength (log10 Ksp0) is -7.5(1) (2σ) (s = 0.05 g·L-1). This is significantly higher than the log10 Ksp0 of witherite of -8.56 (s = 0.01 g·L-1), supporting the disordered nature of the major Ra(Ba)CO3 phase. The limited co-precipitation of Ra2+ within witherite, the significantly higher solubility of pure RaCO3 compared to witherite, and thermodynamic modeling show that the results obtained in this work for the major Ra(Ba)CO3 phase are also applicable to pure RaCO3. The refinement of the EXAFS data reveals that radium is coordinated by nine oxygens in a broad bond distance distribution with a mean Ra-O bond distance of 2.885(3) Å (1σ). The Ra-O bond distance gives an ionic radius of Ra2+ in a 9-fold coordination of 1.545(6) Å (1σ).

Atomic structure of a nudivirus occlusion body protein determined from a 70-year-old crystal sample

Infectious protein crystals are an essential part of the viral lifecycle for double-stranded DNA Baculoviridae and double-stranded RNA cypoviruses. These viral protein crystals, termed occlusion bodies or polyhedra, are dense protein assemblies that form a crystalline array, encasing newly formed virions. Here, using X-ray crystallography we determine the structure of a polyhedrin from Nudiviridae. This double-stranded DNA virus family is a sister-group to the baculoviruses, whose members were thought to lack occlusion bodies. The 70-year-old sample contains a well-ordered lattice formed by a predominantly α-helical building block that assembles into a dense, highly interconnected protein crystal. The lattice is maintained by extensive hydrophobic and electrostatic interactions, disulfide bonds, and domain switching. The resulting lattice is resistant to most environmental stresses. Comparison of this structure to baculovirus or cypovirus polyhedra shows a distinct protein structure, crystal space group, and unit cell dimensions, however, all polyhedra utilise common principles of occlusion body assembly.

A combined theoretical and experimental study of the D-2-aminobutyric acid L-norvaline single crystal for efficient third-order nonlinear optical (NLO) applications

Here we report, the formation of an optically active single crystal of D-2-aminobutyric acid L-Norvaline (ABANV) by the slow evaporation technique by co-crystallization of amino acids D-2-aminobutyric acid (ABA) and L-Norvaline together in water. An X-ray diffraction technique has been used to determine the dimensions of the single crystal unit cells. The functional group of ABANV crystal was studied using FTIR spectroscopy in order to determine its chemical structure. The FT NMR spectrum was conducted to analyze the carbon and hydrogen environments of the grown crystal. In optical absorption studies, the crystal was shown to be transparent in the visible region with a lower cut off wavelength of 236 nm, which led to an optical band gap energy Eg of 5.25 eV. In addition, using TG/DSC techniques, we have investigated the thermal stability of the grown ABANV single crystal as well as their accurate melting point. A HOMO and LUMO analysis were performed to determine the electronic charge distribution and reactivity of the molecules within the crystal. First-order molecular hyperpolarizality (β) properties of the grown crystal have been determined using the B3LYP method. The scatter graph provides an explanation of the chemical bonding of ELF and LOL, as well as the inter and intra fragment interactions.

Study on photocatalytic, electric, and sensing behavior of Co- and Ag-codoped tin dioxide (SnO2) nano particles

In the current work, the role of Co and Ag co-doping on the electric, optical, and sensing performance of tin dioxide nano particles was investigated. Hydrothermally (co-)precipitation of the dopants was utilized to fabricate pure SnO2 and Sn0.96-xCo0.04AgxO2 (x = 0, 0.02, 0.04) nanoparticles. The crystal structure and microstructure of SnO2 particles was almost unchanged although Co-Ag co-doping reduced particle size from 51.8 nm to 41.6 nm and the unit cell dimensions changed. Overall, Co and Ag resulted in significant rise in oxygen vacancy of SnO2 so that defects compensate unbalanced electron charge induced by dopants. It was also figured out that Co-Ag co-doping improved the conductivity of dioxide at low and high temperatures. Doping Led to decrement in the band gap energy of tin dioxide from 3.66 eV to 3.07 eV, which shows improved optical properties of the compound. Study on photodegradation activity of SnO2 showed up to 97 % enhancement due to Co-Ag co-doping. Finally, the sensor response of the compound revealed that the response intensity of tin dioxide increased significantly when 4 wt % Co and 2 wt % Ag are doped into it.

Auxetic incisions with alternating slit shapes: a promising technique for enhancing synthetic skin grafts expansion

Split thickness skin grafts are widely used in treating burn injuries. To date, with limited availability of donor skin and minimal expansions offered by conventional skin grafting, it is challenging to cover large and severe burns. In this study, novel synthetic skin grafts with alternating slit (AS) shaped cut patterns were developed and tested to evaluate the expansion potentials offered by auxetic or negative Poisson’s ratio structures in skin grafting. A range of auxetic incision patterns were designed with varying unit cell dimensions, and these were projected onto skin using 3D printing. The mechanical properties and digital image correlation of the created synthetic skin grafts were used to determine stress, effective Poisson’s ratio, meshing ratio (MR), and generated strains for strain loadings of up to 150%. The AS graft simulant with equal slit lengths and low slit spacings exhibited the maximum negative Poisson’s effect, expansion, and Mr Expansions were inversely related with the spacing between slits. The lowest value for the MR and highest stress was observed with high spacing, high horizontal slit length, and low vertical slit length. The expansions were highly sensitive to the applied strain, with low strains exhibiting high auxeticity. Such an extensive experimental investigation of the expansion potentials and stress estimations of skin grafts with varying AS dimensional parameters have not been conducted previously. The findings would be crucial for advancing research on mitigation of large burn injuries using high expansion skin grafts.

A Study of Dielectric Effects on Resonance Frequency of a Spit Ring Shaped Inclusion

Resonator designs are central to the development of subwavelength unit structures of metasurfaces to create exotic and unique electromagnetic properties by modifying the host structure to tune impinging electromagnetic waves. The act of intentional control of propagating electromagnetic fields are actively being explored in wireless radio environment control for sixth generation (6G) and beyond. In this paper, we study the effect of dielectric properties on electric field distribution and resonance frequency of a circular split ring resonator (SRR). The subwavelength resonator structure is modelled and simulated using High Frequency Structure Simulation (HFSS) software. Rogers RO3003 and RO3210 were used at different thickness to study the field distribution and its effect on resonance frequency of the SSR. The results show a decrease in resonance frequency of 38.41% from RO3002 (lower relative permeability of 3) to RO3210 (higher relative permeability of 10.2). With change in Rogers RO3210 thickness from 1mm to 1.525mm, the resonance frequency has changed from 5.5GHz to 5.2313 GHz. This indicates that the material composition of the substrate and the physical dimension of the SRR unit cell affects the resonance frequency of the structure.   &nbsp

Reexamine the emergence and stability of the square cylinder phase in block copolymers.

Recently, a few AB-type multiblock copolymers have been successfully designed to form stable square cylinder phase based on self-consistent field theory (SCFT) calculations. The previous works only identify the stability region of the square phase but not analyzing its stability, which is closely related to the free-energy landscape. In this work, we have reexamined the stability of the square phase in $\mathrm{B_1 A_1 B_2 A_2 B_3}$ linear pentablock and $\mathrm{(B_1AB_2)_5}$ star triblock copolymers by drawing the free-energy landscape with respect to the two dimensions of a rectangular unit cell. Our results demonstrate that the square phase continuously transfers to the rectangular phase as the degree of packing frustration is gradually released. Moreover, the prolate contour lines of the free-energy landscape indicate the weak stability of the square phase in the $\mathrm{B_1 A_1 B_2 A_2 B_3}$ copolymer. In contrast, the stability of the square phase is notably improved in the $\mathrm{(B_1AB_2)_5}$ copolymer due to its enhanced concentration of bridging configurations. Our work sheds light on the understanding of the stability of the square cylinder phase in block copolymers. Accordingly, we propose some possible strategies for further designing new AB-type block copolymer systems to obtain more stable square phase.

Comparison of the performances between the gray and non-gray media approaches of thermal transport in silicon-tin

We have compared the performances of the gray and non–gray media approaches of thermal transport in Silicon – Tin using Monte Carlo Simulation. The Boltzmann Transport Equation (BTE) for phonons was used to describe the heat flow and ballistic conduction in semiconducting alloy systems. In this work, we have attempted solving the BTE using Monte Carlo (MC) simulation Computational domains for both gray and non-gray media approaches are modeled and the geometry and dimensions of unit cell and sub-cells in the domain are determined. In addition, the computational performances of the gray and non-gray media approaches are compared. The results revealed that when compared to non- gray approach, the gray media approach has more errors in the sub-cells. The maximum relative error is about 3.5%. The results also show that the non–gray media approach of thermal transport in Silicon – Tin exhibited numerical predictions with a very close match to experimental data.

Polarization insensitive multiband metasurface absorber for L, C, and X band applications

An ultrathin, multiband, polarization insensitive with wide angle stability metasurface absorber having unitcell dimension is proposed ( is the free space wavelength at 1.6 GHz). The four-fold symmetry of the unitcell makes it insensitive to TE and TM polarizations. This metasurface follows the sub-quarter wavelength thickness including an air gap of 2.5 mm and metal backing. The proposed unitcell of the metamaterial absorber (MMA) is designed by parametric optimization and has absorption peaks in L, C, and X bands. This absorber is suitable for applications like radar cross section reduction, isolation, and stealth technologies. The lumped SMD resistors are used to enhance absorption peaks simultaneously in all bands mentioned above. This metasurface has absorptivity of 95%, 99%, 97% & 94% at 1.6 GHz, 5 GHz, 7.5 GHz and 10.2 GHz respectively. This is a polarization-insensitive absorber showing stable absorption for different incidence angles between and at the above-given frequencies. The absorption effect has been studied by investigating the filter effect from the equivalent circuit modeling using surface current distribution and normalized impedance. The proposed structure has been fabricated and its measurement results agree well with the simulated one.

Scattering suppression with dual-band single-layer mantle cloak for cylindrical metasurface

This paper investigates scattering suppression with a dual-band and single-layer mantle cloak by using the proper structure for cylindrical objects. The mantle cloak’s surface impedance is calculated according to the Mie Theory to obtain considerable scattering reduction at all angles of the cylinder. The analytical formulation assists in determining the proper unit cell dimensions to obtain design parameters. Firstly, the patch array geometry is applied on the mantle cloak for a single operating frequency with different unit cell numbers. Then a new design of a dual-band single-layer mantle cloak is made with the findings obtained. Simulations are conducted for both mantle cloaks, and bi-static Radar Cross-Section (RCS) analyses are carried out, generating simulated outcomes for cylinders that are both cloaked and uncloaked. The comparison of the scattering suppression between them reveals that the cloaked cylinders demonstrate a significant reduction in scattering. These achievements apply to both single-band and dual-band designs. A novel dual-band single-layer mantle cloak is presented with a new design method and scattering suppression is observed in more than one operating frequency. As evidence of the subject, a dual-band cloaked cylinder is designed with a total radius of 0.13λ0, a total length of 2.59λ0, and a thin dielectric layer’s thickness of 0.0127λ0(λ0i s the wavelength at design frequency f0=3 GHz). This dual-band cloaked cylinder has 7.6 dB absolute RCS reduction at f=2.05 GHz and 5.6 dB absolute RCS reduction at f=3.75 GHz. An efficient scattering suppression is achieved for these two different frequencies in all directions. The considerable degree of invisibility observed in this study opens up possibilities for future investigations in various fields, including radar applications, sensing applications, and antenna isolation for the purpose of blockage reduction.

Andrieslombaardite, RhSbS, a new platinum-group mineral from the platiniferous Onverwacht Pipe, Republic of South Africa

Abstract A hundred years after the discovery of the Merensky Reef in 1924, it is appropriate to present the new mineral andrieslombaardite in honour of Andries Frederik Lombaard who was instrumental in its discovery. Andrieslombaardite, RhSbS, was first described as an unknown mineral from placer deposits associated with the Tulameen Alaskan-Uralian type complex, British Colombia, Canada (Raicevic and Cabri, 1976) but has since been reported from several other deposits including the platiniferous Driekop, Mooihoek, and Onverwacht pipes in the eastern Bushveld Complex, South Africa. The mineral and the name were approved by the Commission on New Minerals Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA no. 2022-076) based on data in the co-type samples from Onverwacht and a co-type sample from the Yubdo stream, Birbir River, Ethiopia. Andrieslombaardite in the Onverwacht sample is a single 8 x 20 μm grain attached to laurite in a matrix of altered silicate and Fe-oxyhydroxide minerals. In the Yubdo samples, there are many grains of pale brownish gray andrieslombaardite up to 25 x 55 μm in size, included in Pt-Fe alloys, some associated with erlichmanite, and others attached to bornite and chalcopyrite. The reflectance values (R%) measured in air and in oil at the COM wavelengths are 48.3 and 33.0 (470 nm), 49.3 and 34.0 (546 nm), 51.0 and 35.9 (589 nm), and 51.8 and 36.7 (650 nm). The colour values x, y, Y, λd, and Pe in air are 0.317, 0.322, 50.3, 580, and 3.2, and in oil are 0.319, 0.324, 35.6, 579, and 4.5. The composition of andrieslombaardite is ideally RhSbS, but it contains variable amounts of Fe, Pt, Pd, and Ir that may substitute for Rh. The mineral is cubic with unit-cell dimensions of a = 6.0278(4) Å, V = 219.01(6) Å3 and Z = 4. It was synthesised at 400 and 550°C using stoichiometric elemental amounts. It is a member of the cobaltite group. The mineralisation of the intrusive dunite pipes was probably introduced at high temperatures, under magmatic conditions. The primary assemblages were to a certain degree overprinted and redistributed by low-temperature hydrothermal fluids. The Pt-Fe alloys from Yubdo containing PGM inclusions such as andrieslombaardite in the Yubdo-Alaskan-type complex were formed at some post-magmatic stage owing to PGE remobilisation during hydrothermal or metamorphic episodes.

Driekopite, Ideally PtBi, a New Mineral Species from the Driekop Platinum Pipe, Republic of South Africa

Abstract The new mineral driekopite, ideally PtBi, was found in a concentrate from the Driekop mine, one of three zoned Pt pipes (mined from 1925 to 1930) that crosscut the layered mafic and ultramafic sequences of the eastern Bushveld Complex, Republic of South Africa. The holotype grain of driekopite (∼ 22 × 13 μm) occurs in a complex, rounded aggregate ∼120 μm in diameter, in association with isoferroplatinum (Pt3Fe), hollingworthite (RhAsS), geversite (PtSb2), insizwaite (PtBi2), andrieslombaardite (RhSbS), stibiopalladinite (Pd5Sb2), sobolevskite (PdBi), possible tatyanaite (Pt9Cu3Sn4), osmium-bearing tulameenite (Pt2FeCu), and Pt-Fe alloy (∼Pt2Fe). Driekopite appears slightly orange under reflected light compared to Pt-Fe alloys. It shows moderate to strong bireflectance, varying from light yellow to brownish yellow, no pleochroism or internal reflections, and moderate to strong anisotropism. The empirical formula, calculated from the average of six wavelength-dispersive spectrometry analyses made on five grains, on the basis of two atoms, is (Pt0.68Pd0.31Fe0.01)Σ1.00(Bi0.53Sb0.43As0.02Sn0.02S0.01)Σ1.01. The mineral is hexagonal, space group P63/mmc (#194) with the refined unit-cell dimensions a = 4.1993(5), c = 5.6194(6) Å, V = 85.82 Å3, Z = 2, and Dcalc = 12.91 g/cm3. Driekopite is isostructural with NiAs, with mixed compositions of Pt and Pd at the 2a site (0.55:0.45, respectively) and Bi and Sb at the 2c site (0.63:0.37, respectively). Its crystal structure was refined to wR = 6.3% using 13 unique Laue reflections obtained using synchrotron radiation. The six strongest lines for the powder X-ray diffraction pattern calculated from the crystal structure refined from synchrotron data is [d in Å (I) (hkl)]: 3.0531 (92) (101), 2.2234 (100) (102), 2.0997 (77) , 1.5266 (28) (202), 1.2347 (24) , 1.1676 (18) . The holotype grain of driekopite is observed to be paragenetically later than isoferroplatinum and hollingworthite and is considered to be synformational with Bi-bearing geversite, insizwaite, andrieslombaardite, and sobolevskite. The entire aggregate containing these platinum-group minerals is overgrown by a rim of tulameenite and Pt-Fe alloy (∼Pt2Fe), indicating they are paragenetically the last minerals to form. Experiments designed to synthesize PtBi over the range of 200 to 500 °C were all successful. Synthetic PtBi melts congruently at 765 °C, suggesting that driekopite likely crystallized at sub-magmatic temperatures.

Atomic-Scale Corrugations in Crystalline Polypeptoid Nanosheets Revealed by Three-Dimensional Cryogenic Electron Microscopy.

Amphiphilic molecules that can crystallize often form molecularly thin nanosheets in aqueous solutions. The possibility of atomic-scale corrugations in these structures has not yet been recognized. We have studied the self-assembly of amphiphilic polypeptoids, a family of bio-inspired polymers that can self-assemble into various crystalline nanostructures. Atomic-scale structure of the crystals in these systems has been inferred using both X-ray diffraction and electron microscopy. Here we use cryogenic electron microscopy to determine the in-plane and out-of-plane structures of a crystalline nanosheet. Data were collected as a function of tilt angle and analyzed using a hybrid single-particle crystallographic approach. The analysis reveals that adjacent rows of peptoid chains, which are separated by 4.5 Å in the plane of the nanosheet, are offset by 6 Å in the direction perpendicular to the plane of the nanosheet. These atomic-scale corrugations lead to a doubling of the unit cell dimension from 4.5 to 9 Å. Our work provides an alternative interpretation for the observed Å X-ray diffraction peak often reported in polypeptoid crystals.

Design of a compact metamaterial absorber with wide angular stability and polarisation insensitive for C, X and broad Ku band applications

Abstract The article presents the design and development of a metamaterial-based microwave absorber having polarisation insensitivity, broad angle of incidence, low profile, and compactness in the microwave frequency range. The unit cell focuses to achieve maximum absorption at C-, X- and broad Ku-bands. The structure is simulated and the results are analysed for different angles of polarisation and angle of incidence. The dimension of the proposed structure is ultrathin and compact having an overall dimension of 8 mm × 8 mm × 0.8 mm. The dimensions are optimized in such a fashion to achieve three different peaks at three different bands thereby making the triple-band behaviour of the metamaterial absorber possible. The structure is providing absorption of 99.14% absorption at 6.08 GHz (C-Band) while absorption of 98.29% is achieved at 9.49 GHz (X-band) and 265 MHz bandwidth with above 95% absorption from 16.57 GHz to 16.83 GHz (Ku-Band) in the microwave regime. The absorber patch is a composition of square ring patches and a central square ring annexed with triangles on four sides, the split ring providing a combinational effect witnessing the desired absorption at designated frequencies. The unit cell dimension at a lower cut-off frequency is 0.162 λ lowest. The proposed structure is verified for polarisation sensitivity and has a wide angle of incidence. The structure is experimentally verified for results and is found to be in close agreement with simulated ones. The compactness of structure with the attainment of the highest form of absorption in different bands including the 265 MHz high absorption band provides the scope of applicability in various engineering applications at microwave regimes.

Experimental and numerical investigation of the static behavior of a 3D printed bio-based anti-trichiral sandwich

In this work, the analysis of the static behavior of the composite honeycomb and anti-trichiral sandwich is studied. The objective of this paper is to estimate the effect of cellular geometrical parameters which are the ligament length and the cylindrical node radius on the static properties of the anti-trichiral structures. The core and the sandwiches were made from the same biobased material which is polylactic acid with flax fibers (Flax/PLA Material). 3D printing technology was used to manufacture the specimens. Several tensile tests were performed on the anti-trichiral core while bending tests were carried out on the sandwich structures. Several specimens with different geometric parameters of the anti-trichiral unit cell are tested to study their effect on the static properties of this material. The results show that the static properties of the anti-trichiral shaped meta-material depend on the unit cell dimensions. The Poisson’s ratio varies from 1 to −1 and from 0.5 to−0.8 respectively for one-cell and two-cell cores in width. To validate the experimental results, numerical simulations were carried out. Experimental and computational results for the Poisson’s ratio were quite similar.