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.     

One-pot synthesis of dihydropyrimidinones catalysed by lithium bromide: an improved procedure for the Biginelli reaction

LiBr catalyses efficiently the three component condensation reaction of an aldehyde, a β-ketoester and urea in refluxing acetonitrile to afford the corresponding dihydropyrimidinones in high yield.     

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.     

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.     

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.     

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.     

Mastering by the teacher of the instrumental genesis in CAS environments: necessity of intrumental orchestrations

In this article, we study didactic phenomena identified in integration experiments within our classes, CAS (implemented in calculators). From this study, we show the interest of an instrumental approach to understand the influence of tools on the mathematical approach and on the building of student's knowledge: through a process—instrumental genesis—a calculator becomes a mathematical work tool; this process depends on the tool's constraints and potentialities, on students' knowledge, and on the class' work situations. To analyze the differentiation of instrumental genesis, we then have taken interest in students' behaviour and we propose a method enabling us to constitute a typology of extreme behaviour in environments of symbolic calculators. To take the variety of these genesis into account, the professor needs a particular organization of space and time of the study in the class. We suggest the notion of instrumental orchestration to name this organization. We demonstrate how this notion gives a better definition of the objectives, the configurations and the exploitation modes of different arrangements which aim at constituting coherent instrument systems for each student and for the class.