Amorphous Formation Research Articles

Improved Ductility of Boron Carbide by Microalloying with Boron Suboxide

Boron carbide (B_4C) is the third hardest material in nature, but applications are hindered by its brittle failure under impact. We found that this brittle failure of B_4C arises from amorphous shear band formation due to deconstruction of icosahedral clusters, and on the basis of this model we suggest and validate with quantum mechanics (QM, PBE flavor of density function theory) that a laminated B_4C–B_6O composite structure will eliminate this brittle failure. Using QM to apply shear deformations along various slip systems, we find that the (001)/[100] slip system has the lowest maximum shear strength, indicating it to be the most plausible slip system. We find that this composite structure has a shear strength of 38.33 GPa, essentially the same as that of B_4C (38.97 GPa), indicating the same intrinsic hardness as B4C. However, the critical failure strain for (001)/[100] slip in the composite is 0.465, which is 41% higher than B_4C, indicating a dramatically improvement on ductility. This arises because incorporation of B_6O prevents the failure mechanism of B_4C in which the carbene formed during shear deformation reacts with the C–B–C chains. This suggests a new strategy for designing ductile superhard ceramics.

Povacoat affecting solid-state polymorphic changes of indomethacin after co-evaporation from different types of solvents via conventional and microwave drying techniques

The effect of Povacoat on the solid state characteristics and polymorphic transformation of γ-form of indomethacin (γ-IMC) after solvent co-evaporation via two drying methods was investigated by thermoanalytical and FTIR spectroscopic studies. The types of solvents (water, ethanol, and water:ethanol (1:9 ~ 2:8, v/v)), weight ratios of Povacoat:IMC (4:1 ~ 4:10, w/w), and drying methods (air-drying and microwave-drying) were selected as variables in this study. A physical mixture of Povacoat and γ-IMC was also carried out by neat grinding process. The results indicate that there was no interaction between Povacoat and γ-IMC or no polymorphic change of γ-IMC after the neat co-grinding process. Since Povacoat was only soluble in water or <30% ethanol aqueous solution but γ-IMC was only soluble in organic solvents, different solvents and drying methods might significantly influence the solid-state characteristics of IMC formed in the presence of Povacoat. It was found that the amorphous IMC was formed in the Povacoat/IMC evaporates after dissolving both Povacoat and γ-IMC in water:ethanol (mixed ratio=1:9 and 2:8, v/v) and co-evaporation via microwave-drying, whereas the α-IMC was formed in the Povacoat/IMC evaporates via the air-drying method. In addition, the predominate α-IMC formation was only found in all the Povacoat/IMC evaporates with different weight ratios prepared by previously dissolving in water:ethanol (1:9, v/v) and co-evaporation via air-drying, but the amorphous IMC formation after co-evaporation via microwave-drying was obtained except the 4:10 (w/w) weight ratio. The thermal effect of microwave irradiation and the presence of Povacoat might be responsible for the amorphous IMC formation in the Povacoat/IMC evaporates.

Rosin Surfactant QRMAE Can Be Utilized as an Amorphous Aggregate Inducer: A Case Study of Mammalian Serum Albumin.

Quaternary amine of diethylaminoethyl rosin ester (QRMAE), chemically synthesized biocompatible rosin based cationic surfactant, has various biological applications including its use as a food product additive. In this study, we examined the amorphous aggregation behavior of mammalian serum albumins at pH 7.5, i.e., two units above their isoelectric points (pI ~5.5), and the roles played by positive charge and hydrophobicity of exogenously added rosin surfactant QRMAE. The study was carried out on five mammalian serum albumins, using various spectroscopic methods, dye binding assay, circular dichroism and electron microscopy. The thermodynamics of the binding of mammalian serum albumins to cationic rosin modified surfactant were established using isothermal titration calorimetry (ITC). It was observed that a suitable molar ratio of protein to QRMAE surfactant enthusiastically induces amorphous aggregate formation at a pH above two units of pI. Rosin surfactant QRMAE-albumins interactions revealed a unique interplay between the initial electrostatic and the subsequent hydrophobic interactions that play an important role towards the formation of hydrophobic interactions-driven amorphous aggregate. Amorphous aggregation of proteins is associated with varying diseases, from the formation of protein wine haze to the expansion of the eye lenses in cataract, during the expression and purification of recombinant proteins. This study can be used for the design of novel biomolecules or drugs with the ability to neutralize factor(s) responsible for the aggregate formation, in addition to various other industrial applications.

Structural changes in histone H2A by methylglyoxal generate highly immunogenic amorphous aggregates with implications in auto-immune response in cancer.

The role of aberrant protein modifications in cancer and its diagnosis have emerged as a promising research field. Nonenzymatic glyco-oxidation of proteins under oxidative stress has been associated with carcinogenesis through advanced glycation end products (AGE)-receptors for advanced glycation end products (RAGE) axis. Modified proteins that are immunogenic and stimulate cellular and humoral immune responses are being studied to develop early detection markers of cancer. This study has probed the structural alternations; leading to the formation of adducts and aggregates, in histone H2A upon in vitro modification by methylglyoxal (MG). The immunogenicity of modified histone H2A and its binding with cancer autoantibodies was also assessed. MG induced lysine side chain modifications, blocking of free amino groups and the formation of condensed cross structures in histone H2A; and its effect was inhibited by carbonyl scavengers. It led to the adduct formation and generation of N-epsilon-(carboxyethyl)lysine (CEL) and its decomposition forms as revealed by Matrix-assisted laser desorption ionization-mass spectrometry, high-performance liquid chromatography and LC-MS. MG-H2A showed amorphous aggregate formation under electron microscopy and altered binding with DNA in circular dichroism studies. The modified histone elicited high titer immunogen-specific antibodies in rabbits when compared with the native, thus pointing toward the generation of neo-epitopes in MG-H2A. The autoantibodies derived from cancer patients exhibited enhanced binding with MG-H2A as compared with the native histone in enzyme-linked immunosorbent assay and gel retardation assay. This reflects sharing of epitopes on MG-H2A and histones in cancer patients. The neo-epitopes on H2A may be responsible for induction and elevated levels of antibodies in cancer patients. Thus, MG-H2A may be considered as potential antigenic candidate for auto-immune response in cancer.

Atomistic Origin of Brittle Failure of Boron Carbide from Large-Scale Reactive Dynamics Simulations: Suggestions toward Improved Ductility.

Ceramics are strong, but their low fracture toughness prevents extended engineering applications. In particular, boron carbide (B(4)C), the third hardest material in nature, has not been incorporated into many commercial applications because it exhibits anomalous failure when subjected to hypervelocity impact. To determine the atomistic origin of this brittle failure, we performed large-scale (∼200,000 atoms/cell) reactive-molecular-dynamics simulations of shear deformations of B(4)C, using the quantum-mechanics-derived reactive force field simulation. We examined the (0001)/⟨101̅0⟩ slip system related to deformation twinning and the (011̅1̅)/⟨1̅101⟩ slip system related to amorphous band formation. We find that brittle failure in B(4)C arises from formation of higher density amorphous bands due to fracture of the icosahedra, a unique feature of these boron based materials. This leads to negative pressure and cavitation resulting in crack opening. Thus, to design ductile materials based on B(4)C we propose alloying aimed at promoting shear relaxation through intericosahedral slip that avoids icosahedral fracture.

Dicarbonyl Induced Structural Perturbations Make Histone H1 Highly Immunogenic and Generate an Auto-Immune Response in Cancer.

Increased oxidative stress under hyperglycemic conditions, through the interaction of AGEs with RAGE receptors and via activation of interleukin mediated transcription signalling, has been reported in cancer. Proteins modifications are being explored for their roles in the development and progression of cancer and autoantibody response against them is gaining interest as a probe for early detection of the disease. This study has analysed the changes in histone H1 upon modification by methylglyoxal (MG) and its implications in auto-immunopathogenesis of cancer. Modified histone showed modifications in the aromatic residues, changed tyrosine microenvironment, intermolecular cross linking and generation of AGEs. It showed masking of hydrophobic patches and a hypsochromic shift in the in ANS specific fluorescence. MG aggressively oxidized histone H1 leading to the accumulation of reactive carbonyls. Far UV CD measurements showed di-carbonyl induced enhancement of the alpha structure and the induction of beta sheet conformation; and thermal denaturation (Tm) studies confirmed the thermal stability of the modified histone. FTIR analysis showed amide I band shift, generation of a carboxyethyl group and N-Cα vibrations in the modified histone. LCMS analysis confirmed the formation of Nε-(carboxyethyl)lysine and electron microscopic studies revealed the amorphous aggregate formation. The modified histone showed altered cooperative binding with DNA. Modified H1 induced high titre antibodies in rabbits and the IgG isolated form sera of rabbits immunized with modified H1 exhibited specific binding with its immunogen in Western Blot analysis. IgG isolated from the sera of patients with lung cancer, prostate cancer, breast cancer and cancer of head and neck region showed better recognition for neo-epitopes on the modified histone, reflecting the presence of circulating autoantibodies in cancer. Since reports suggest a link between AGE-RAGE axis and carcinogenesis, glycoxidation of histone H1 and its immunogenicity paves ways for understanding role of glycoxidatively damaged nuclear proteins in cancer.

Investigation of various phases of Fe–Si structures formed in Si by low energy Fe ion implantation

The compositional phases of ion beam synthesized Fe–Si structures at two high fluences (0.50×1017atoms/cm2 and 2.16×1017atoms/cm2) were analyzed using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The distribution of Fe implanted in Si was simulated using a dynamic simulation code (TRIDYN) incorporating target sputtering effects. The Fe depth profiles in the Si matrix were confirmed with Rutherford backscattering spectrometry (RBS) and XPS depth profiling using Ar-ion etching. Based on XPS binding energy shift and spectral asymmetry, the distribution of stable Fe–Si phases in the substrate was analyzed as a function of depth. Results indicate Fe implantation with a fluence of 0.50×1017atoms/cm2 and subsequent thermal annealing produce mainly the β-FeSi2 phase in the whole thickness of the implanted region. But for the samples with a higher fluence Fe implantation, multiple phases are formed. Significant amount of Fe3Si phase are found at depth intervals of 14nm and 28nm from the surface. Initially, as-implanted samples show amorphous Fe3Si formation and further thermal annealing at 500°C for 60min formed crystalline Fe3Si structures at the same depth intervals. In addition, thermal annealing at 800°C for 60min restructures the Fe3Si clusters to form FeSi2 and FeSi phases.

Fabrication of Transparent Nanohybrids with Heat Resistance Using High-Density Amorphous Formation and Uniform Dispersion of Nanodiamond.

A new technology for the production of transparent material using a "crystalline" polymer is proposed in the present study. Further, transparent and flexible crystalline polymer nanohybrid film containing well-dispersed nanodiamond filler was fabricated. Partially fluorinated crystalline polymer with switchboard-type lamellae results in high transparency as a consequence of the formation of a high-density amorphous structure based on high-temperature drawing just below the melting point at 110 °C. Although the formation of nanohybrid materials composed of fluorinated-polymer/organo-modified nanocarbon is generally difficult, we confirmed the formation, via melt-compounding, using atomic force microscopy and wide-angle X-ray diffraction. Even though the polymer matrix/nanodiamond hybrid has remarkable aggregation properties, a well-dispersed state was achieved because of improvement in wettability obtained through surface modification of filler. The resulting nanohybrid demonstrates transparency, increased thermal degradation temperature, and enhanced mechanical properties, which seem to be derived from the nucleation effect caused by the adsorption of the terminal polymer chain onto the organic modifier.

Radiation effects in astrophysical ices

The interaction of heavy ions with astrophysical ices was studied at different beamlines of GANIL by infrared absorption spectroscopy. This allowed simulating in the laboratory the physico-chemical modifications induced in icy objects in space, exposed to radiation fields such as the solar wind, magnetospheric particles and interstellar cosmic rays. We briefly discuss sputtering, destruction and formation of molecules, amorphization and compaction, implantation, and finally the formation of organic molecules. This latter topic is related to the question of the initial conditions for the emergence of life.

Electrochemical hydrogen storage behaviors of the nanocrystalline and amorphous Nd-Cu-added Mg2Ni-type alloy electrodes applied to Ni-MH battery

In order to ameliorate the electrochemical characteristics of Mg2Ni-type alloy, the elements Cu and Nd are added in the alloy. The nanocrystalline and amorphous Mg2Ni-type alloys with the composition of (Mg24Ni10Cu2)100–xNdx (x = 0, 5, 10, 15, 20) are prepared by melt spinning technology. The effects of Nd content and spinning rate on structures and electrochemical performances of the alloys are investigated. X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveal that the as-spun Nd-free alloy displays an entirely nanocrystalline structure, whereas the as-spun Nd15 alloy, differing from Nd0 alloy, exhibits nanocrystals embedded in an amorphous matrix. This suggests that the addition of Nd facilitates the amorphous formation ability of the alloys. The electrochemical measurement indicates that both adding Nd and melt spinning significantly improve the electrochemical performances of the alloys, involving the discharge potential characteristics, discharge capacity, cycle stability, and the high rate dischargeability (HRD). The Nd addition and melt spinning enhance the diffusion ability of hydrogen atoms in the alloy, but both of them impair the charge-transfer ability on the surface of the alloy electrode, which gives rise to the HRD values first mounting up and then going down with the growing of the Nd content and the spinning rate.

Novel Water-Soluble Substrate for Silicateins

We suggested to use tetrakis(2-hydroxyethyl)orthosilicate (THEOS) as a substrate for silicateins--an enzyme family playing a key role in formation of skeleton in marine sponges. We compared THEOS with tetraethylorthosilicate (TEOS)--a commonly used substrate for silicateins. These substrates were tested in reaction of amorphous silica formation in vitro catalyzed by silicatein Al from sponge Latrunculia oparinae. It was found that reaction with THEOS occurs more efficiently than with TEOS, probably due to high water solubility and higher hydrolysis rate of THEOS.

Preparation, in vitro mineralization and osteoblast cell response of electrospun 13-93 bioactive glass nanofibers.

In this study, silicate based 13-93 bioactive glass fibers were prepared through sol-gel processing and electrospinning technique. A precursor solution containing poly (vinyl alcohol) and bioactive glass sol was used to produce fibers. The mixture was electrospun at a voltage of 20 kV by maintaining tip to a collector distance of 10 cm. The amorphous glass fibers with an average diameter of 464±95 nm were successfully obtained after calcination at 625 °C. Hydroxyapatite formation on calcined 13-93 fibers was investigated in simulated body fluid (SBF) using two different fiber concentrations (0.5 and 1 mg/ml) at 37 °C. When immersed in SBF, conversion to a calcium phosphate material showed a strong dependence on the fiber concentration. At 1mg/ml, the surface of the fibers converted to the hydroxyapatite-like material in SBF only after 30 days. At lower solid concentrations (0.5 mg/ml), an amorphous calcium phosphate layer formation was observed followed by the conversion to hydroxyapatite phase after 7 days of immersion. The XTT (2,3-Bis-(2-Methoxy-4-Nitro-5-Sulfophenyl)-2H-Tetrazolium-5-Carboxanilide) assay was conducted to evaluate the osteoblast cell response to the bioactive glass fibers.

Si-doped nano- and microcrystalline diamond films with controlled bright photoluminescence of silicon-vacancy color centers

Nanocrystalline diamond (NCD) and microcrystalline diamond (MCD) films with bright photoluminescence (PL) of silicon-vacancy (SiV) color centers at 738nm have been grown using a microwave plasma CVD technique. The films were doped with Si via adding silane to CH4–H2 reaction gas mixture in the course of the deposition process. The dependence of SiV PL intensity on silane concentration in gas shows a maximum at SiH4/CH4 ratios of 0.2% and 0.6% for NCD and MCD films, respectively, the maximum intensity for MCD being an order of magnitude stronger compared with that for NCD. The PL quenching at higher CH4 addition occurs, however, no significant degradation of the film structure, such as Si-induced amorphous carbon formation, was observed within the SiH4 concentration range studied (0%–0.9%). The higher PL efficiency of the MCD films is related to their less defective structure, as deduced from Raman spectroscopy analysis.

Visible light communications in heterogeneous networks: Paving the way for user-centric design

At the time of this writing, there is substantial research interest in the subject of visible light communications (VLC) owing to its ability to offer significant traffic offloading potential in highly crowded radio frequency (RF) scenarios. We introduce the user-centric design of VLC for heterogeneous networks (HetNet), where three key aspects are identified and elaborated on: signal coverage quality, system control, and service provision aspects. More explicitly, the concepts of amorphous cell formation as well as separated up-link (UL) and down-link (DL), decoupled data and control, dynamic load balancing (LB), etc., all demand radically new thinking. The advocated user-centric VLC design is of key significance in the small-cell scenarios of the emerging 5G design philosophy.

α-Al2O3 nanoslab fracture and fatigue behavior

Strain rate effects and cyclic loading behavior, relevant for fatigue initiation processes, of single crystalline α-Al2O3 nanoslab structures in vacuum have been characterized and compared under finite temperature dynamic loading and incremental static loading conditions by reactive molecular dynamics and ionic relaxation simulations, respectively. Different failure mechanisms for each loading case are observed and compared in view of known applicable material failure mechanisms. In particular, structure size effects along with unit cell and bulk defect distribution based mechanisms are considered. The effects of lateral pre-strain are assessed. Conclusions are drawn regarding conditions which could lead to low cycle failure of the material.The results indicate that finite temperature and strain rate result in lower failure strains, as compared to static relaxation calculations, however low strength enhancement of ductility with kinematic strain hardening upon repeated loading may occur. We suggest that the latter facilitates a shakedown mechanism. Positive pre-straining results in increased stress triaxiality (hydrostatic vs. equivalent stress), which significantly reduces crack healing probability, due to single sharp crack propagation. Instead, volume pre-relaxation results in multiple crack branching and/or amorphous band formation, which facilitates crack healing and deformation induced transition to purely elastic response (shakedown) possibility. Amorphization, which manifests as small strain plasticity enhancement, is found to occur ahead of propagating cracks due to multiple dislocation mechanism as a low energy barrier partially reversible low density phase transition, both at static and finite temperature/strain rate conditions. The observed property changes and phase change related defect healing mechanisms have been investigated further by bulk unit cell simulations and validated against DFT calculations.

Resistive switching of reactive sputtered TiO2 based memristor in crossbar geometry

In this work, TiO2 based metal/metal oxide/metal memristor structures are investigated using I–V–t measurements. TiO2 films are deposited to pre-patterned area using a lift-off technique. Bottom and top metallization are done using Pt and Ti RF-sputtering, and 10nm thick active TiO2 layer is grown by reactive RF sputter at room temperature. Amorphous film formation is observed by XRD measurements. Initial high resistance state-of-films lead us to fabricate memristors in matrix form using photolithography. We note that although measurements carried out at room temperatures demonstrated a well-pinched behavior, during the continuous loop the resistance of structure under the test steadily increased after each scanning polarity change. A step-like resistance change is observed by application of periodic DC pulses. This change was step like for the first 20s. time duration but turned to a random manner for the prolonged time.

Morphology of calcium silicate hydrate (C-S-H) gel: a molecular dynamic study

Due to its complexity at nanoscale, calcium silicate hydrate (C-S-H), the dominant binding phase in cement hydrates, is not yet completely understood. In this study, molecular dynamics was employed to simulate the hydration products at low and high calcium/silicon ratios. It was found that two morphologies of calcium silicate hydrate gels can be distinguished – a branched structure at low calcium/silicon ratios and an ellipsoid particle structure at high calcium/silicon ratios. Using virtual X-ray diffraction (XRD), nuclear magnetic resonance (NMR) and small-angle neutron scattering (SANS) techniques, the simulated structures were characterised, confirming that they show features of calcium silicate hydrate as revealed by experimental approaches. The short-range structures of calcium and silicon atoms and the distorted calcium tetrahedrons resemble the features of silicate glasses obtained from experiments, implying the amorphous nature of the local structure in calcium silicate hydrate gel. Furthermore, formation mechanisms for the two morphologies are proposed. In the hydration process, calcium ions play roles in depolymerising the silicate structure and preventing the amorphous network formation. Therefore, at low calcium/silicon ratios, the reaction is governed by silicate skeleton growth, but at high calcium/silicon ratio, aggregations of calcium ions and short silicate chains dominate.

A multi-pathway perspective on protein aggregation: Implications for control of the rate and extent of amyloid formation

The nucleation-growth model has been used extensively for characterizing in vitro amyloid fibril formation kinetics and for simulating the relationship between amyloid and disease. In the majority of studies amyloid has been considered as the dominant, or sole, aggregation end product, with the presence of other competing non-amyloid aggregation processes, for example amorphous aggregate formation, being largely ignored. Here, we examine possible regulatory effects that off-pathway processes might exert on the rate and extent of amyloid formation – in particular their potential for providing false positives and negatives in the evaluation of anti-amyloidogenic agents. Furthermore, we investigate how such competing reactions might influence the standard interpretation of amyloid aggregation as a two-state system. We conclude by discussing our findings in terms of the general concepts of supersaturation and system metastability – providing some mechanistic insight as to how these empirical phenomena may manifest themselves in the amyloid arena.

Analysis of Magnetic Take-Up Roll Employed in Amorphous Alloy Ribbon Production Line

A novel magnetic take-up roll used in amorphous alloy ribbon formation lines is introduced in this paper. The finite element method was used to calculate two different magnetic models for a selected amorphous ribbon. The simulation result showed that magnetic adhesion force can make the ribbon move toward and stay on the magnetic take-up roll. The tests indicated that the results measured complied with simulation ones. Moreover, the final design prototype test successfully satisfy the main objective of the project – to take up the ribbon – with a high success rate.

Unraveling the Core of The Gran Pirámide From Cholula, Puebla. A Compositional and Microstructural Analysis of the Adobe

ABSTRACTThe Gran Pirámide, a Mexican cultural heritage site, is located at the archaeological site of Cholula, Puebla, Mexico. At the base of its platform this pyramid is the largest in the world. It was built in layers from 800 to 1100 AD by the Cholultecan pre-Hispanic culture. The archaeological site is famous by its great mural paintings that have been well-studied. The pyramid was built with earthen construction, a system of multiple bulding episodes with layers of adobe. The building material, adobe, has not been well studied. Due to its fragile condition, a more extensive study was conducted to understand the behavior of the building and the mural paintings substrate, in order to propose conservation strategies.Geological context of the area was the starting point to propose the relevant materials used in its construction. That was a fundamental key for the interpretation of the experimental techniques used that include X-ray Diffraction (XRD), Particle-Induced X-ray Emission (PIXE), 29Si and 27Al Nuclear-Magnetic Resonance with Magic-Angle Spin (NMR-MAS), Thermal Analysis, Optical and Scanning Electron Microscopy (SEM) and colorimetric measurements.The results obtained from the original adobes have been compared with fresh soils from horizons related with pre-Hispanic activity. The results indicate presence of amorphous materials and neo-mineral formation besides feldspars and opal. The amorphous phases have been identified by NMR-MAS and SEM.Differences were found in the composition from the adobe used for the joints, mainly in the clay fraction, that can be distinguished by color and that guided to group the information acquired.These results provide new information on the composition and microstructure of adobes from the Gran Pirámide of Cholula. Further studies will involve soil physics methods and erosion tests to complete the task of having a comprehensive knowledge of the earth architecture of the pyramid.