Push-pull [2]pseudorotaxanes. Electronic control of threading by switching ON/OFF an intramolecular charge transfer

[reaction: see text] Addition of acid and base allows switching between two different structures in a push-pull bis(pyridinium)ethane axle, controlling its ability to form [2]pseudorotaxanes with a dibenzo-24-crown-8 ether wheel.     

Radiative heat transfer at nanoscale: Closed-form expression for silicon at different doping levels

Radiative heat transfer at the nanoscale is becoming an important technological issue with the development of nano electromechanical systems (NEMS). In this article, we derive asymptotic expressions to compute near-field radiative heat transfer between two planes of silicon. We identify two physical mechanisms that give the dominant contribution at small gaps. For intrinsic and low-doped silicon, the main contribution is due to evanescent waves coming from propagating waves undergoing frustrated total internal reflections at the interfaces. For doping levels larger than N_e=10¹⁶ cm^?3 surface mode coupling contributes to the heat transfer. Asymptotic expressions are also given in that case. In all cases, we compare analytical formulas with exact numerical calculations when varying the temperature and the doping concentration. We also give their range of validity.     

Use of 4-bromo pyridazine 3,6-dione for building 3-amino pyridazine libraries

An efficient method for preparation of 4,6 or 5,6 disubstituted 3-aminopyridazines was easily carried out starting from easily available 4-bromo-pyridazine-3,6-dione, and using combination of both amination and Pd(0) cross-coupling reactions under microwave irradiation.     

Interstack Interactions in Potassium Bis(1,2-Cyclobutenedione 3,4-dithiolato) Palladate. Crystal Structure

Abstract

Potassium bis(1,2-cyclobutenedione 3,4-dithiolato) palladate (Pd(dithiosquarato)₂K₂) crystallizes in the monolinic system, space group P2₁/c, a = 8.046(2), b = 15.235(4), c = 6.289(1). The dithiosquarate entities are stacked in parallel columns separated by potassium cations and water molecules. π-interactions within a stack are evidenced by the short stacking distance (3.51 Å). Further interstack interactions involve close S…O or O…O interstack contacts. (～3.5 Å). As a result, the structural arrangement is nearly two-dimensional. Conductivity measurements carried out on pressed pellets show a semi-conductive behavior (σ = 2 × 10^?5 Ω^?1 cm¹).     

A numerical evaluation of Rayleigh's theory applied to scattering by randomly rough dielectric surfaces

Abstract

We present a numerical simulation of scattering by one-dimensional randomly rough surfaces. It is based on the use of plane-wave expansions to describe the Melds on the surface (i.e. Rayleigh hypothesis). Accuracy and convergence properties of two different numerical implementations are studied. Some examples of results for a dielectric and a metallic Gaussian rough surface are shown to be in good agreement with calculations by a rigorous numerical method. The Rayleigh method appears to be a fast computation tool for dielectric surfaces with slopes of less than 0.2.     

Brightening of an accretion disk due to viscous dissipation of gravitational waves during the coalescence of supermassive black holes

Mergers of supermassive black hole binaries release peak power of up to approximately 10(57) erg s(-1) in gravitational waves (GWs). As the GWs propagate through ambient gas, they induce shear and a small fraction of their power is dissipated through viscosity. The dissipated heat appears as electromagnetic (EM) radiation, providing a prompt EM counterpart to the GW signal. For thin accretion disks, the GW heating rate exceeds the accretion power at distances farther than approximately 10(3) Schwarzschild radii, independently of the accretion rate and viscosity coefficient.     

Possibility of precise measurement of the cosmological power spectrum with a dedicated survey of 21 cm emission after reionization

Measurements of the 21 cm line emission by residual cosmic hydrogen after reionization can be used to trace the power spectrum of density perturbations through a significant fraction of the observable volume of the Universe. We show that a dedicated 21 cm observatory could probe a number of independent modes that is 2 orders of magnitude larger than currently available, and enable a cosmic-variance limited detection of the signature of a neutrino mass approximately 0.05 eV. The evolution of the linear growth factor with redshift could also constrain exotic theories of gravity or dark energy to an unprecedented precision.     

Image encryption based on fractional chaotic pseudo-random number generator and DNA encryption method

Nonlinear Dynamics - Nonlinear dynamic systems and chaotic systems have been quite exhaustively researched in the domain of cryptography. However, the possibility of using fractional chaotic...     

Template-directed excimer formation via specific non-covalent interactions between pyrene guanidinium derivatives and nucleic acids

Structurally distinct guanidinium derivatives were evaluated for their ability to interact non-covalently with various nucleic acid sequences. Among the evaluated derivatives, 4-[(pyrene-1-ylmethyl)amino]butyl] guanidinium (pbg) was found to demonstrate strong excimer emission upon nucleic acid addition and high levels of discrimination between ds- and ss-DNA. The intensity of excimer emission proved to be dependent on the length of the linker probe as well as the oligonucleotide length and sequence. In particular, G-quadruplex prone structures were found to induce the highest excimer emissions among all nucleic acids tested.     

Stereospecific cyclodehydration of 1,4-sulfanylalcohols to thiolanes: mechanistic insights

A series of thiolanes were prepared by cyclodehydration of sulfanylalcohols in the presence of catalytic amounts of p-toluenesulfonic acid or by using K10 clay. The sulfur heterocycles were synthesised in good to excellent yields using either a conventional Dean-Stark method or microwave irradiation under solvent-free conditions. The reaction could be performed regio- and stereoselectively and its mechanism was investigated by means of enantio- and diastereomerically enriched substrates. In contrast to previous studies, our results are consistent with an intramolecular S_N2-type mechanism as a general pathway.