Locally enhanced dissolution rate as a probe for nanocontact-induced densification in oxide glasses

Atomic force microscopy (AFM) was used to characterize the surface damage (nanoindentations) effect on the chemical durability of glass surfaces (silica and soda-lime silicate glasses, WG). In basic solutions, an enhanced dissolution rate is reported and quantified at indentation sites (+10.5 nm/h and +52 nm/h for silica and WG, respectively) whereas none was observed once the indented surfaces were thermally annealed at 0.9 × T(g) for 2 h, a thermal treatment known for curing high pressure-induced permanent densification in oxides glasses. A direct link between high pressure-induced structural modifications encountered during nanoindentation and the measured dissolution rates is established. It is shown that this property conjointly used with the high resolution of the atomic force microscope may be used for probing, at the nanometer scale, the size and the nature of the structurally modified area underneath residual nanoindentation impressions. As an example, for 10 mN Vickers nanoindentations on WG, the zone affected by the permanently and structurally modified zone under the residual impression is found to be equal to (741 ± 30) nm with a transition zone thickness from the fully densified material to the elastically deformed one ranging between 115 and 165 nm.     

Nuclear quadrupole interaction at 181Ta in hafnium dioxide fiber: Time differential perturbed angular correlation measurements and ab initio calculations

The thermal behavior of hafnium dioxide fiber has been investigated with the aid of time differential perturbed angular correlation (TDPAC) technique along with XRD and SEM measurements. This study has proved a good thermal stability of the fibrous material up to 1173 K and the fiber loses its crystallinity to a meager extent at 1673 K. No phase transition has been observed up to 1673 K in this fiber. TDPAC parameters for the HfO₂ fiber annealed at 1173 K are ω_Q=124.6 (3) Mrad/s and η=0.36 (1). These values remain unaltered for the HfO₂ fiber annealed even at 1673 K. Electronic structure calculations based on the density functional theory (DFT) for HfO₂ doped with tantalum impurity have been performed and the calculated EFG parameters are in reasonable agreement with the experimental values.     

Durability of an As2S3 chalcogenide glass: Optical properties and dissolution kinetics

The durability of a As₂S₃ chalcogenide glass composition was studied in de-ionized water at different temperatures (60-90 °C) for different periods of time, up to 120 days. The evolutions of the chemical composition and the pH of the solutions as well as the optical transmission of bulk samples, in the 2-10 μm region, were measured as a function of corrosion time. Atomic force microscopy and optical microscopy were used to investigate the roughness of corroded surfaces and the evolution of surface defects. The water corrosion of As₂S₃ glass was found to follow a congruent dissolution mechanism, a possible glass-water reaction mechanism was proposed. The optical transmission of the glass was found to be affected by the corrosion. The optical loss increased from 4 to 21% with corrosion time, this variation was attributed to the texturation of the surface by the reaction of corrosion. Moreover, the experimental results show that high temperature value enhances the corrosion reaction: an activation energy of 103 ± 2 kJ/mol was computed from experimental measurements.     

A selective adenosine sensor derived from a triplex DNA aptamer

The aim of this study is to develop a selective adenosine aptamer sensor using a rational approach. Unlike traditional RNA aptamers developed from SELEX, duplex DNA containing an abasic site can function as a general scaffold to rationally design aptamers for small aromatic molecules. We discovered that abasic site-containing triplex DNA can also function as an aptamer and provide better affinity than duplex DNA aptamers. A novel adenosine aptamer sensor was designed using such a triplex. The aptamer is modified with furano-dU in the binding site to sense the binding. The sensor bound adenosine has a dissociation constant of 400 nM, more than tenfold stronger than the adenosine aptamer developed from SELEX. The binding quenched furano-dU fluorescence by 40%. It was also demonstrated in this study that this sensor is selective for adenosine over uridine, cytidine, guanosine, ATP, and AMP. The detection limit of this sensor is about 50 nM. The sensor can be used to quantify adenosine concentrations between 50 nM and 2 μM.     

Thermo‐Responsive MOF/Polymer Composites for Temperature‐Mediated Water Capture and Release

We report an in situ polymerization strategy to incorporate a thermo‐responsive polymer, poly(N‐isopropylacrylamide) (PNIPAM), with controlled loadings into the cavity of a mesoporous metal–organic framework (MOF), MIL‐101(Cr). The resulting MOF/polymer composites exhibit an unprecedented temperature‐triggered water capture and release behavior originating from the thermo‐responsive phase transition of the PNIPAM component. This result sheds light on the development of stimuli‐responsive porous adsorbent materials for water capture and heat transfer applications under relatively mild operating conditions.     

Linear algebraic techniques to construct monochrome visual cryptographic schemes for general access structure and its applications to color images

Though the monochrome (black and white) visual cryptography has a very rich literature, a very few papers have been published for the construction of general access structure. In this paper we put forward a method of construction of a strong monochrome visual cryptographic scheme (VCS) for general access structure using linear algebra. As a particular case of general access structure, \((k,n)\) -VCS for \(2 \le k \le n\) is obtained. The \((n,n)\) -VCS obtained from the scheme attains the optimal pixel expansion as well as optimal relative contrast. We provide an efficient construction of \((n-1,n)\) -VCS. We further extend our monochrome VCS to color VCS for restricted access structures. Finally, we provide some interesting examples that will lead to some future research directions in the area of VCS.     

A mild and efficient method for the protection of carbonyl compounds as oxathiolanes, dithiolanes and dithianes catalyzed by molybdenyl acetylacetonate

Carbonyl compounds have been successfully converted into their corresponding oxathiolane, dithiolane and dithiane derivatives in excellent yields with 2-mercaptoethanol, 1,2-ethanedithiol and 1,3-propanedithiol using a catalytic amount of molybdenyl acetylacetonate.     

Advantage of Fractional Calculus Based Hybrid‐Theoretical‐Computational‐Experimental Approach for Alternating Current Voltammetry

The dynamic electrochemical behavior of electroactive species is believed to be represented better by the fractional calculus, because it can consider the history of mass‐transfers of that species near the electrode surface. The elucidation of mathematical fundamentals of fractional calculus has been recently introduced for batteries, supercapacitors and a few voltammetry studies. The working equations for faradaic fundamental and second‐harmonic (SHac) components of alternating current (ac) for ac voltammetry of an electrochemically reversible redox reaction on an electrode of macroscopic diameter have been derived here by using generalized formulae of the fractional calculus. A computation code is written in Python language with a matrix based algorithm developed based on latest, accurate, efficient and stable Grunwald‐Letnikov‐Improved fractional‐order differentiation equation. That computational code is used to find the concealed faradaic fundamental, SHac components of the total current and other double‐layer parameters of experimentally recorded voltammograms of ruthenium(III/II) redox reaction on gold‐disc electrode by a common electrochemical workstation without having inbuilt Fourier transformation features. The amplitude of the computed faradaic current concealed in the experimental data gets enhanced through this hybrid theoretical‐computational‐experimental approach and thus it keeps scope of application and further improvement in electroanalysis.     

Anion‐Responsive Tunable Bulk‐Phase Homochirality and Luminescence of a Cationic Framework

Reaction of a linear bi‐chelating N‐donor achiral ligand with Zn^II afforded a homochiral cationic framework with six‐fold one‐dimensional helical chains. The compound showed selective anion exchange behavior with interesting anion‐responsive tunable bulk‐phase homochirality. The cationic framework also presented anion‐driven variable luminescence and sorption behavior.