Orders Of Magnitude Higher Resistance Research Articles

Silica-based planar lightwave circuits with high resistance against blue light for visible-light application

We propose two novel types of waveguide, Zr-doped and non-doped silica, for high-power visible-light applications. We fabricated these waveguides and investigated their resistance against blue light. Both Zr-doped and non-doped silica waveguides showed one order of magnitude higher resistance against blue light compared with conventional Ge-doped silica waveguides. A comparison of their resistances indicated that Zr-doped silica waveguides are useful against blue light powers up to about 20 mW and non-doped silica waveguides have more potential for higher resistance against blue light powers over 20 mW.

Формування наногетерогенних матеріалів з підвищеними показниками жаростійкості

The work performed the researches, aimed at creating compositions - nanoheterogeneous materials with increased characteristics of heat resistance. A critical analysis of widely studied brands of coatings from the standpoint of modern materials science was conducted, at the result of what was shown that many of the applied heterogeneous nanostructured protective coatings can be recognized as neither rational in composition nor the best in properties. Of the known groups of materials with special physical and chemical properties, the least studied are nanostructured nanoheterogeneous coatings, due to the lack of a rigorous theory and the presence of criteria selected for its evaluation. Therefore, the aim of the work became a develop general principles for obtaining rational compositions of nanoheterogeneous coatings with increased characteristics of high heat resistance. Nickel was chosen as the basis for the heterogeneous coating. The results of the study of the protective nanoheterogeneous coating of the Ni–Al–Ti–C–SiO2–Al2O3–B2O system are presented. The proposed coatings differ in that they have an order of magnitude higher resistance to oxidation compared to stainless steel. Wear intensity indicators remain virtually unchanged over the entire temperature range and are much lower than traditionally used wear-resistant materials. At the change of speed of sliding in the conditions of the increased loadings intensity of wearing remains practically invariable and is twice less in comparison with coverings of tungsten carbide. Keywords: heat-resistant coatings, alloy, oxidation resistance, wear intensity, heat resistance

Secreted Expression of mRNA-Encoded Truncated ACE2 Variants for SARS-CoV-2 via Lipid-Like Nanoassemblies.

The transfer of foreign synthetic messenger RNA (mRNA) into cells is essential for mRNA‐based protein‐replacement therapies. Prophylactic mRNA COVID‐19 vaccines commonly utilize nanotechnology to deliver mRNA encoding SARS‐CoV‐2 vaccine antigens, thereby triggering the body's immune response and preventing infections. In this study, a new combinatorial library of symmetric lipid‐like compounds is constructed, and among which a lead compound is selected to prepare lipid‐like nanoassemblies (LLNs) for intracellular delivery of mRNA. After multiround optimization, the mRNA formulated into core–shell‐structured LLNs exhibits more than three orders of magnitude higher resistance to serum than the unprotected mRNA, and leads to sustained and high‐level protein expression in mammalian cells. A single intravenous injection of LLNs into mice achieves over 95% mRNA translation in the spleen, without causing significant hematological and histological changes. Delivery of in‐vitro‐transcribed mRNA that encodes high‐affinity truncated ACE2 variants (tACE2v mRNA) through LLNs induces elevated expression and secretion of tACE2v decoys, which is able to effectively block the binding of the receptor‐binding domain of the SARS‐CoV‐2 to the human ACE2 receptor. The robust neutralization activity in vitro suggests that intracellular delivery of mRNA encoding ACE2 receptor mimics via LLNs may represent a potential intervention strategy for COVID‐19.

Effect of substitution and impurities on dielectric properties and resistivity of CaCu3Ti4O12

The authors have performed the synthesis and grain growth of pure calcium copper titanate (CaCu3Ti4O12 or CCTO) compound and its derivatives by substituting silicon CaCu3SixTi4−xO12 (CCSTO) to determine the effect on dielectric properties and resistivity. The authors observed significant increase in the resistivity even with small concentration of silicon. Concentration above 5% did not produce any significant advantages; they also observed a similar increase in resistivity when CCSTO is doped with nickel. In a separate experiment, the authors soaked the CCSTO before grain growth in an organic melt. Soaking also increased the resistivity by several orders of magnitude. The authors observed almost three orders of magnitude higher resistivity in CCSTO compared with CCTO material processed under identical conditions.

Cloning, mutagenesis, and characterization of the microalga Parietochloris incisa acetohydroxyacid synthase, and its possible use as an endogenous selection marker

Parietochloris incisa is an oleaginous fresh water green microalga that accumulates an unusually high content of the valuable long-chain polyunsaturated fatty acid (LC-PUFA) arachidonic acid within triacylglycerols in cytoplasmic lipid bodies. Here, we describe cloning and mutagenesis of the P. incisa acetohydroxyacid synthase (PiAHAS) gene for use as an herbicide resistance selection marker for transformation. Use of an endogenous gene circumvents the risks and regulatory difficulties of cultivating antibiotic-resistant organisms. AHAS is present in plants and microorganisms where it catalyzes the first essential step in the synthesis of branched-chain amino acids. It is the target enzyme of the herbicide sulfometuron methyl (SMM), which effectively inhibits growth of bacteria and plants. Several point mutations of AHAS are known to confer herbicide resistance. We cloned the cDNA that encodes PiAHAS and introduced a W605S point mutation (PimAHAS). Catalytic activity and herbicide resistance of the wild-type and mutant proteins were characterized in the AHAS-deficient E. coli, BUM1 strain. Cloned PiAHAS wild-type and mutant genes complemented AHAS-deficient bacterial growth. Furthermore, bacteria expressing the mutant PiAHAS exhibited high resistance to SMM. Purified PiAHAS wild-type and mutant proteins were assayed for enzymatic activity and herbicide resistance. The W605S mutation was shown to cause a twofold decrease in enzymatic activity and in affinity for the Pyruvate substrate. However, the mutant exhibited 7 orders of magnitude higher resistance to the SMM herbicide than that of the wild type.

Structural bolstering of metal sites as nodes in metal–organic frameworks

We show that a metal site attains orders of magnitude higher resistance (compared to its molecular form) towards external ligand-induced disruption of its coordination environment upon incorporation as the building block of a crystalline metal–organic framework (MOF).

Microstructure Evolution During Plasma Electrolytic Oxidation and Its Effects on the Electrochemical Properties of AZ91D Mg Alloy

The microstructure development during plasma electrolytic oxidation (PEO) and its influence on the electrochemical corrosion properties of AZ91D Mg alloy were investigated. PEO was conducted in a KF-NaAlO2 electrolyte, and the corrosion properties of PEO coatings were evaluated by potentiodynamic and potentiostatic tests and electrochemical impedance spectroscopy (EIS). At the breakdown voltage, a non-porous, fluoride-containing barrier-type layer with less-crystalline MgAl2O4 and MgF2 was formed. With the intense sparking, a porous layer appeared at the surface. The outer porous layer was a nearly amorphous oxide. The inner dense layer was composed of nano-crystalline MgAl2O4 and MgF2, and its fluoride content and crystallinity increased with PEO time. The existence of MgF2 phase in the innermost layer was clearly demonstrated by high resolution transmission electron microscopy (HRTEM). The potentiodynamic tests indicated that the corrosion potential (Ecorr) remained relatively constant, but the corrosion current density (icorr) significantly decreased with PEO time. The EIS results revealed that ∼2 orders of magnitude higher resistance of inner dense layer mainly contributed to the improved corrosion resistance of AZ91D Mg alloy. The enhanced corrosion resistance with the progress of PEO was discussed in terms of thickness, fluoride content, and crystallinity of inner dense layer.

Effects of Crystal Phase Mixing on the Electrical Properties of InAs Nanowires

We report a systematic study of the relationship between crystal quality and electrical properties of InAs nanowires grown by MOVPE and MBE, with crystal structure varying from wurtzite to zinc blende. We find that mixtures of these phases can exhibit up to 2 orders of magnitude higher resistivity than single-phase nanowires, with a temperature-activated transport mechanism. However, it is also found that defects in the form of stacking faults and twin planes do not significantly affect the resistivity. These findings are important for nanowire-based devices, where uncontrolled formation of particular polytype mixtures may lead to unacceptable device variability.

Gas Sensors: Ultrasensitive and Highly Selective Gas Sensors Based on Electrospun SnO2 Nanofibers Modified by Pd Loading (Adv. Funct. Mater. 24/2010)

AbstractThis work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO2 fibers. Unloaded and Pd‐loaded SnO2 nanofiber mats are synthesized by electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO2 crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO2 crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO2 grain growth during the calcination step. The Pd‐loaded SnO2 sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H2 and lower sensitivity to NO2 compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO2 crystallites and catalytic effect of PdO in promoting the oxidation of H2 into H2O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.

Ultrasensitive and Highly Selective Gas Sensors Based on Electrospun SnO2 Nanofibers Modified by Pd Loading

AbstractThis work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO2 fibers. Unloaded and Pd‐loaded SnO2 nanofiber mats are synthesized by electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO2 crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO2 crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO2 grain growth during the calcination step. The Pd‐loaded SnO2 sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H2 and lower sensitivity to NO2 compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO2 crystallites and catalytic effect of PdO in promoting the oxidation of H2 into H2O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.

Corrosion Resistance and Antibacterial Properties of Ag-Containing MAO Coatings on AZ31 Magnesium Alloy Formed by Microarc Oxidation

Silver-containing oxide coatings on AZ31 Mg alloys were fabricated by microarc oxidation (MAO) in -containing sodium silicate -based electrolyte, and their physical and chemical properties were investigated, particularly focusing on corrosion resistance and antibacterial activity. The porous oxide coatings consisting of and MgO formed in both -containing and -free electrolytes and the MAO coatings were composed of a porous outer layer and a dense inner layer. MAO in -containing electrolyte resulted in a thicker oxide coating, especially a thicker fluorine (F)-rich inner layer. Fluorine (F) was rich in the dense inner layer, and Ag was preferentially located close to the coating surface. The potentiodynamic test indicated that Ag-containing MAO coating had a more positive corrosion potential (−1.42 V), lower corrosion current density , and thus higher corrosion resistance compared to Ag-free MAO coatings (−1.53 V, , and , respectively). The electrochemical impedance spectroscopy results revealed that the higher corrosion resistance of Ag-containing MAO coating was due to an order of magnitude higher resistance of the dense inner layer. Ag-containing MAO coating showed an excellent antibacterial activity over 99.9% against two strains of bacteria, Staphylococcus aureus and Escherichia coli.

Viscoelasticity and high buckling stress of dense carbon nanotube brushes

We report on the mechanical behavior of a dense brush of small-diameter (1–3 nm) non-catalytic multiwall (2–4 walls) carbon nanotubes (CNTs), with ∼10 times higher density than CNT brushes produced by other methods. Under compression with spherical indenters of different radii, these highly dense CNT brushes exhibit a higher modulus (∼17–20 GPa) and orders of magnitude higher resistance to buckling than vapor phase deposited CNT brushes or carbon walls. We also demonstrate the viscoelastic behavior, caused by the increased influence of the van der Waals’ forces in these highly dense CNT brushes, showing their promise for energy-absorbing coatings.

Effect of growth parameters on the morphology and resistivity of PbSe

A series of lead selenide (PbSe) films were produced by the physical vapor transport (PVT) method. It was observed that substrate temperature and source purity have a pronounced effect on the morphology, resistivity, and crystallinity. As the substrate temperature increased, the crystal orientation changed from (1 1 1) to the (0 0 1) orientation. High-quality films, with a full-width at half-maxima as low as 0.3°, were grown. Further, the electrical resistivity could be changed by annealing the samples in air or by film impurity content. Annealing in an oxygen atmosphere produced three orders of magnitude higher resistivity compared to pure PbSe material. The virgin material showed 60.7 kΩ cm and annealed sample showed a resistivity value of 5.0 MΩ cm.

Tunneling and enhanced magnetoresistance in Nd2/3Sr1/3MnO3 thin films with microcracks

We found that microcracks in thin Nd2/3Sr1/3MnO3 films create a series of intrinsic break junctions which are ideal for investigating tunneling phenomena in this system. A comparison of films with and without cracks, which have similar ferromagnetic Curie temperature (Tc) of 140–150 K, shows that the cracked film has a lower insulator to metal transition temperature TM (97 K vs 140 K), three orders of magnitude higher resistivity at TM, and two times larger magnetoresistance at 1 T near TM. At T>TM we observed that ln ραT−1/4 in the uncracked film while in the cracked film a ln ραT−1/2 dependence was found. This indicates that the conductivity in the first case is due to variable range hopping in three dimension, while in the second case it is dominated by thermally activated tunneling across the insulating barriers (the microcracks).

High resistivity LT-In0.47Ga0.53P grown by gas source molecular beam epitaxy

Low-temperature (LT) growth of In0.47Ga0.53P was carried out in the temperature range from 200 to 260°C by gas source molecular beam epitaxy using solid Ga and In and precracked PH3. The Hall measurements of the as-grown film showed a resistivity of ∼106 Ω-cm at room temperature whereas the annealed film (at 600°C for 1 h) had at least three orders of magnitude higher resistivity. The Hall measurements, also, indicated activation energies of ∼0.5 and 0.8 eV for the asgrown and annealed samples, respectively. Double-crystal x-ray diffraction showed that the LT-InGaP films had ∼47% In composition. The angular separation, Δθ, between the GaAs substrate and the as-grown LT-InGaP film on (004) reflection was increased by 20 arc-s after annealing. In order to better understand the annealing effect, a LT-InGaP film was grown on an InGaP film grown at 480°C. While annealing did not have any effect on the HT-InGaP peak position, the LT-InGaP peak was shifted toward the HT-InGaP peak, indicating a decrease in the LT-InGaP lattice parameter. Cross-sectional transmission electron microscopy indicates the presence of phase separation in LT-InGaP films, manifested in the form of a “precipitate-like” microstructure. The analytical scanning transmission electron microscopy analysis of the LT-InGaP film revealed a group-V nonstoichiometric deviation of ∼0.5 at.% P. To our knowledge, this is the first report about the growth and characterization of LT-InGaP films.

Radiation damage of BGO crystals due to low energy γ rays, high energy protons and fast neutrons

Results are presented on the effects of radiation on BGO crystals. It is shown that BGO has more than two orders of magnitude higher resistance against low energy γ rays than SF5 lead glass. Darkening of the crystal is hardly visible even after an irradiation of 3.6 × 10 6 R. The darkening faded by more than one half after several days and it has almost completely disappeared after much longer periods. The tolerable rate of synchrotron radiation on BGO calorimeters is 100 R/h in a conservative estimate if the degradation in transmittance is required to be less than 1 % over a depth of 20 radiation lengths. In BGO calorimeters, the degradation of scintillation efficiency is less important than that of the transmittance, 99.999% pure crystals have a two orders of magnitude better resistance than 99.99% pure ones. Sample darkening caused by 12 GeV protons or fast neutrons is an order of magnitude more severe than that by low energy γ rays. Moreover, the recovery is not complete even after a period of more than 100 days. Some data on sample activation are also presented.