Passivation of pinhole defect microelectrode arrays in ultrathin silica films immobilized on gold substrates

Nanoscopic defects present in ultrathin (~ 6 nm) silica films covalently attached to gold substrates through a gold oxide layer exhibit a voltammetric response consistent with a random array of ultramicroelectrodes. These pinholes can be passivated via electrochemical polymerization of phenol to create insulating poly(phenylene) oxide plugs as documented by atomic force microscopy and infrared reflectance-absorbance spectroscopy. Passivation of pinholes is ~ 99.5% complete after 550 voltammetric cycles of oxidative electropolymerization.     

Diffusion of polymer chains in porous media. A Monte Carlo study

In order to determine the structure and the dynamical properties of branched polymers in a random environment an idealized model was developed and studied by means of the Monte Carlo method. All atomic details were suppressed and the chain was represented as a sequence of identical beads. The model chains were star-branched with three arms of equal length. The chains were embedded to a simple cubic lattice and the polymer systems were confined between two parallel surfaces. The confining surfaces were attractive for polymer segments. A set of irregular obstacles was also introduced into the slit which can be viewed as a model of porous media. A Metropolis sampling algorithm employing local changes of chain conformation was used to sample the conformational space. It was shown that the mean dimensions of the chain depend strongly on the strength of surface's attraction and the concentration of obstacles. It was found that the size of the chains scales with the exponent close to the 2-dimensional case rather than to the 3-dimensional system. The long-time (diffusion) dynamic properties of the system were studied. The differences in the mobility of chains depending on the confinement, on the filling of the slit and on the internal macromolecular architectures were shown and discussed. The possible mechanism of chain's motion was shown: during the migration of the chain in the obstacles dense environment it can be trapped in the region of local lower density of obstacles (a ‘cavity’) and after some time it can leave the place moving into another cavity.     

Three-dimensional modeling of the I-TevI homing endonuclease catalytic domain, a GIY-YIG superfamily member, using NMR restraints and Monte Carlo dynamics

Using a recent version of the SICHO algorithm for in silicoprotein folding, we made a blind prediction of the tertiarystructure of the N-terminal, independently folded, catalyticdomain (CD) of the I-TevI homing endonuclease, a representativeof the GIY–YIG superfamily of homing endonucleases. Thesecondary structure of the I-TevI CD has been determined usingNMR spectroscopy, but computational sequence analysis failedto detect any protein of known tertiary structure related tothe GIY–YIG nucleases (Kowalski et al., Nucleic AcidsRes., 1999, 27, 2115–2125). To provide further insightinto the structure–function relationships of all GIY–YIGsuperfamily members, including the recently described subfamilyof type II restriction enzymes (Bujnicki et al., Trends Biochem.Sci., 2000, 26, 9–11), we incorporated the experimentallydetermined and predicted secondary and tertiary restraints ina reduced (side chain only) protein model, which was minimizedby Monte Carlo dynamics and simulated annealing. The subsequentlyelaborated full atomic model of the I-TevI CD allows the availableexperimental data to be put into a structural context and suggeststhat the GIY–YIG domain may dimerize in order to bringtogether the conserved residues of the active site.     

Mechanism of ?-caprolactone polymerization and ?-caprolactone/trimethylene carbonate copolymerization carried out with Zr(Acac)4

The paper presents the mechanism of the polymerization of ?-caprolactone with the use of Zr(Acac)₄. At the first stage of the initiation of the polymerization, a reaction consisting of proton transfer from caprolactone to acetylacetonate ligand and then ligand exchange reaction with release of free acetylacetone (HAcac) occur. Complex 1, arisen as a product of this reaction, is the actual initiator of the observed polymerization. During the conducted polymerization the molar mass increase is directly proportional to monomer conversion degree. On the basis of observed phenomenon, the polymerization of cyclic trimethylene carbonate (TMC) applying ?-caprolactone as a co-initiator is possible. Complex 1 arose in the initial phase of this reaction as well, being an equally efficient initiator for TMC polymerization. Using Zr(Acac)₄ as an initiator for an ?-caprolactone/TMC copolymerization resulted in obtaining a series of copolymers with varied, predicted composition and high molar mass values.     

Optimum deposition conditions of ultrasmooth silver nanolayers

Reduction of surface plasmon-polariton losses due to their scattering on metal surface roughness still remains a challenge in the fabrication of plasmonic devices for nanooptics. To achieve smooth silver films, we study the dependence of surface roughness on the evaporation temperature in a physical vapor deposition process. At the deposition temperature range 90 to 500 K, the mismatch of thermal expansion coefficients of Ag, Ge wetting layer, and sapphire substrate does not deteriorate the metal surface. To avoid ice crystal formation on substrates, the working temperature of the whole physical vapor deposition process should exceed that of the sublimation at the evaporation pressure range. At optimum room temperature, the root-mean-square (RMS) surface roughness was successfully reduced to 0.2 nm for a 10-nm Ag layer on sapphire substrate with a 1-nm germanium wetting interlayer. Silver layers of 10- and 30-nm thickness were examined using an atomic force microscope (AFM), X-ray reflectometry (XRR), and two-dimensional X-ray diffraction (XRD2).

PACS

63.22.Np Layered systems; 68. Surfaces and interfaces; thin films and nanosystems (structure and nonelectronic properties); 81.07.-b Nanoscale materials and structures: fabrication and characterization     

In Silico Study on Tumor-Size-Dependent Thermal Profiles inside an Anthropomorphic Female Breast Phantom Subjected to Multi-Dipole Antenna Array

Electromagnetic hyperthermia as a potent adjuvant for conventional cancer therapies can be considered valuable in modern oncology, as its task is to thermally destroy cancer cells exposed to high-frequency electromagnetic fields. Hyperthermia treatment planning based on computer in silico simulations has the potential to improve the localized heating of breast tissues through the use of the phased-array dipole applicators. Herein, we intended to improve our understanding of temperature estimation in an anatomically accurate female breast phantom embedded with a tumor, particularly when it is exposed to an eight-element dipole antenna matrix surrounding the breast tissues. The Maxwell equations coupled with the modified Pennes’ bioheat equation was solved in the modelled breast tissues using the finite-difference time-domain (FDTD) engine. The microwave (MW) applicators around the object were modelled with shortened half-wavelength dipole antennas operating at the same 1 GHz frequency, but with different input power and phases for the dipole sources. The total input power of an eight-dipole antenna matrix was set at 8 W so that the temperature in the breast tumor did not exceed 42 °C. Finding the optimal setting for each dipole antenna from the matrix was our primary objective. Such a procedure should form the basis of any successful hyperthermia treatment planning. We applied the algorithm of multi for multi-objective optimization for the power and phases for the dipole sources in terms of maximizing the specific absorption rate (SAR) parameter inside the breast tumor while minimizing this parameter in the healthy tissues. Electro-thermal simulations were performed for tumors of different radii to confirm the reliable operation of the given optimization procedure. In the next step, thermal profiles for tumors of various sizes were calculated for the optimal parameters of dipole sources. The computed results showed that larger tumors heated better than smaller tumors; however, the procedure worked well regardless of the tumor size. This verifies the effectiveness of the applied optimization method, regardless of the various stages of breast tumor development.     

Characteristics of LaCo0.4Ni0.6-xCuxO3-δ ceramics as a cathode material for intermediate-temperature solid oxide fuel cells

In this study, the effects of Cu-ion substitution on the densification, microstructure, and physical properties of LaCo_0.4Ni_0.6-xCu_xO_3-δ ceramics were investigated. The results indicate that doping with Cu ions not only enhances the densification but also promotes the grain growth of LaCo_0.4Ni_0.6-xCu_xO_3-δ ceramics. The Cu substitution at x ≤ 0.2 can suppress the formation of La₄Ni₃O₁₀, while the excess Cu triggers the formation of La₂CuO_4.032 phase. The p-type conduction of LaCo_0.4Ni_0.6O_3-δ ceramic was significantly raised by Cu substitution because the acceptor doping ($\begin{array}{c}\hfill \begin{array}{c}\hfill \begin{array}{c}\hfill \begin{array}{c}\hfill C{u}_{Ni}^{\text{'}}\hfill \end{array}\hfill \end{array}\hfill \end{array}\hfill \end{array}$) triggered the formation of hole carriers; this effect was maximized in the case of LaCo_0.4Ni_0.4Cu_0.2O_3-δ composition (1480 S cm^?1 at 500 °C). Thermogravimetric data revealed a slight weight increase of 0.29% for LaCo_0.4Ni_0.4Cu_0.2O_3-δ compact up to 871 °C; this is due to the incorporation of oxygen that creates metal vacancies and additional $\begin{array}{c}\hfill \begin{array}{c}\hfill \begin{array}{c}\hfill \begin{array}{c}\hfill \begin{array}{c}\hfill h^{?}\hfill \end{array}\hfill \end{array}\hfill \end{array}\hfill \end{array}\hfill \end{array}$carriers, partially compensating the conductivity loss due to the spin-disorder scattering. As the temperature of the LaCo_0.4Ni_0.4Cu_0.2O_3-δ compacts rose above 871 °C, significant weight loss with temperature was observed because of the release of lattice oxygen to the ambient air as a result of Co (IV) thermal reduction accompanied by the formation of oxygen vacancies. A solid oxide fuel cell (SOFC) single cell with Sm_0.2Ce_0.8O_2-δ (electrolyte) and LaCo_0.4Ni_0.4Cu_0.2O_3-δ (cathode) was built and characterized. The Ohmic (0.256 Ω cm²) and polarization (0.434 Ω cm²) resistances of the single cell at 700 °C were determined; and the maximum power density was 0.535 W cm^?2. These results show that LaCo_0.4Ni_0.4Cu_0.2O_3-δ is a very promising cathode material for SOFC applications.     

Nonlinear Absorption of Submicrometer Grain‐Size Cobalt‐Doped Magnesium Aluminate Transparent Ceramics

Transparent cobalt‐doped magnesium aluminate spinel (Co:MgAl₂O₄) ceramics with a submicrometer grain size were prepared by spark plasma sintering. For the first time, the nonlinear absorption of Co:MgAl₂O₄ transparent ceramics was experimentally demonstrated. Both ground state absorption (σ_GSA) and excited state absorption (σ_ESA) were estimated using the solid‐state slow saturable absorber model based on absorption saturation measurements performed at 1.535 μm. σ_GSA and σ_ESA for 0.03 at.% Co:MgAl₂O₄ were found to be 4.1 × 10^?19 cm² and 4.0 × 10^?20 cm², respectively. In the case of 0.06 at.% Co:MgAl₂O₄ ceramics, σ_GSA = 2.6 × 10^?19 cm² and σ_ESA= 5.3 × 10^?20 cm² were determined.     

Synthesis and characterization of cross‐linked poly(sodium acrylate)/sodium silicate hydrogels

Transparent and intumescent polymer‐silicate hydrogels were synthesized by free‐radical polymerization, in the presence of the redox initiators system (potassium persulphate/sodium thiosulphate) and cross‐linking monomer (N,N′‐methylenebisacrylamide). Hydrogels obtained in such a manner were rheologically tested and it was found that the same sample with a different sodium acrylate concentration polymerized faster when its content was lower. The spectroscopic and thermal analysis proved that the polymer combines with sodium silicate by hydrogen bonds and during thermal degradation only small polymer fragments and water molecules were released. NMR studies have shown that the content of water glass causes shorter relaxation times. Conducted fire tests showed that glass panes systems filled with the tested hydrogels meet the relevant construction standards and what is their big advantage, a thin 1 mm layer of polymer‐silicate gel is sufficient for this purpose. We believe that these results will contribute to the development of intumescent hydrogels with enhanced fire‐retardant properties. POLYM. ENG. SCI., 59:1279–1287 2019. © 2019 Society of Plastics Engineers