Inversion of the direction of stereoinduction in the coupling of chiral gamma,delta-unsaturated Fischer carbene complexes with o-ethynylbenzaldehyde

[reaction: see text] A variety of gamma,delta-unsaturated carbene complexes that feature a stereogenic center at the beta-carbon couple with 2-ethynylbenzaldehyde to afford hydrophenanthrene derivatives with a high degree of stereoinduction. The direction of stereoinduction is opposite for examples where the stereogenic center is acyclic vs examples where it is within a ring.     

Structural investigation and Hirshfeld surface analysis of two polymorphs of 2-(4-Methylbenzamido)-5-(4-fluoro-3-phenoxyphenyl)-1,3,4-thiadiazoles

In this report, the crystal structure of a new polymorphic form of 2-(4-Methylbenzamido)-5-(4-fluoro-3-phenoxyphenyl)-1,3,4-thiadiazole have been investigated and compared with the previously reported form. Crystallization experiments from a non-polar solvent resulted in the formation of a newly obtained polymorph of this substituted 1,3,4 thiadiazole compound. Structural differences and similarities in both the polymorphic forms were explored in terms of supramolecular building blocks present in the crystal packing and their influences on the supramolecular construct are investigated in terms of the nature and energetics of the associated interactions. In addition, Hirshfeld surface analysis and calculations on the enrichment ratio were carried out for both the forms to isolate the various types of interatomic contacts and differentiate their contribution towards the molecular assembly, as obtained from 2D fingerprint plots. Also, the interaction energies were computed for the new polymorph and compared with the reported form. The studies render quantitative insights into the role of strong H-bonds and weak intermolecular interactions acting cooperatively in the crystal. In addition, the role of both electrostatic and dispersion energies contributes to the overall stability in the crystal packing.     

Low temperature effects on electrical and optical properties of TTBNc thin films

Electrical and optical properties of thermally evaporated air annealed Tetra-Tert-Butyl 2,3 Naphthalocyanine (TTBNc) thin films are studied. From the Arrhenius plot, the thermal activation energy is calculated for intrinsic and extrinsic region. Different hopping conduction parameters are tabulated using the Variable Range Hopping (VRH) model in the low temperature region. The studies on the optical absorption spectra lead to the determination of optical band gap energy and Urbach’s energy of TTBNc thin films. Also the temperature dependence of steepness parameter is explained.     

Ion-induced multiply reentrant liquid-liquid transitions and the nature of criticality in ethanol-water mixture

We report a quite unusual feature of four liquid-liquid reentrant transitions in ethanol (E)+water (W)+ammonium sulfate mixture by meticulous tuning of the ammonium sulfate concentration in a narrow range, as a function of temperature, at atmospheric pressure. Detailed exploration of the intricate phase behavior in terms of E/W sections shows that the range of triple reentrance shrinks with increasing E/W. The behavior of osmotic susceptibility is investigated by light scattering, near the critical point, in the one-phase region by varying the temperature at fixed concentration of the components, in a particular E/W section. The critical exponent of susceptibility (gamma) and correlation length (nu) are observed to have Fisher renormalized Ising values [Phys. Rev. 176, 237 (1968)], with gamma(r)=1.41 and nu(r)=0.718. The effective susceptibility exponent, gamma(eff), exhibits a sharp, nonmonotonic crossover from Ising to mean-field critical behavior, which is completed outside the critical regime. The amplitude of the correlation length, xi(o)(=21.2+/-0.4 A), deduced from light scattering experiment, is an order of magnitude larger than the typical values in usual aqueous electrolyte systems. This value of xi(o) is further verified from small-angle x-ray scattering (SAXS) experiments and found to be consistent. SAXS experiments on the critical sample reveal the presence of long-ranged intermolecular correlations, leading to supramolecular structuring, at a temperature far away from the critical point. These results convincingly demonstrate that the finite length scale arising due to the structuring competes with the diverging correlation length of critical concentration fluctuations, which influences the nonasymptotic critical behavior in this aqueous electrolyte system. The sulphate ions play a dominant role in both structuring and the complex phase behavior.     

Structure, stability, and quantum conductivity of small diameter silicon nanowires

Structures and energetics of various types of silicon nanowires have been investigated using both quantum and classical molecular dynamics simulations to determine the most stable forms. The tetrahedral type nanowires have been found to be the most stable and, surprisingly, the polycrystalline forms of nanowires, while having the smallest surface to bulk ratio, are found to be the least stable. We also show that the cagelike nanowires have greater thermal stability than the tetrahedral nanowires. Furthermore, their electrical conducting properties are found to be better than those of tetrahedral nanowires, suggesting useful molecular electronic applications.     

Preparation and TSL studies in Tb activated LiMgPO4 phosphor

LiMgPO₄:Tb³⁺ phosphor was synthesized by solid state reaction. The thermally stimulated luminescence (TSL) glow curve of Tb doped LiMgPO₄ exhibits a main TSL peak at 170 °C with shoulders at 100 and 260 °C on either side of this peak. The TSL sensitivity of the phosphor was found to be about 2.5 times that of CaSO₄:Dy phosphor. TSL emission and photoluminescence (PL) studies show that Tb³⁺ ion acts as luminescence centre in this phosphor. The kinetic parameters, namely activation energy (E) and frequency factor (s) associated with the main glow peak have been determined using peak shape method. The activation energy and frequency factor obtained are 1.35 ± 0.03 eV and (6.53 ± 0.43) × 10¹⁴ s^?1 respectively. The paper discusses the dosimetric characteristics like dose response, fading, energy response and minimum detectable dose and results thereof.     

Role of mesoscopic morphology in charge transport of doped polyaniline

In doped polyaniline (PANI), the charge transport properties are determined by mesoscopic morphology, which in turn is controlled by the molecular recognition interactions among polymer chain, dopant and solvent, Molecular recognition plays a significant role in chain conformation and charge delocalization. The resistivity of PANI doped by camphor sulfonic acid (CSA)/2-acrylo-amido-1-propane sulfonic acid (AMPSA)/dodecyl benzene sulfonic acid (DBSA) is around 0.02 Ω cm. PANI-CSA and PANI-AMPSA show a metallic positive temperature coefficient of resistivity above 150 K. with a finite value of conductivity at 1.4 K; whereas, PANI-DBSA shows hopping transport at low temperatures. The magnetoresistance is positive (negative) for PANI-CSA (PANI-AMPSA); and PANI-DBSA has a large positive MR. The behavior of MR suggests subtle variations in mesoscopic morphology between PANI-CSA and PANI-AMPSA.     

Vorticity,backscatter and counter-gradient transport predictions using two-level simulation of turbulent flows

The two-level simulation (TLS) method evolves both the large-and the small-scale fields in a two-scale approach and has shown good predictive capabilities in both isotropic and wall-bounded high Reynolds number (Re) turbulent flows in the past. Sensitivity and ability of this modelling approach to predict fundamental features (such as backscatter, counter-gradient turbulent transport, small-scale vorticity, etc.) seen in high Re turbulent flows is assessed here by using two direct numerical simulation (DNS) datasets corresponding to a forced isotropic turbulence at Taylor’s microscale-based Reynolds number Re_λ ≈ 433 and a fully developed turbulent flow in a periodic channel at friction Reynolds number Re_τ ≈ 1000. It is shown that TLS captures the dynamics of local co-/counter-gradient transport and backscatter at the requisite scales of interest. These observations are further confirmed through a posteriori investigation of the flow in a periodic channel at Re_τ = 2000. The results reveal that the TLS method can capture both the large- and the small-scale flow physics in a consistent manner, and at a reduced overall cost when compared to the estimated DNS or wall-resolved LES cost.     

The Building Game: From Enumerative Combinatorics to Conformational Diffusion

We study a discrete attachment model for the self-assembly of polyhedra called the building game. We investigate two distinct aspects of the model: (i) enumerative combinatorics of the intermediate states and (ii) a notion of Brownian motion for the polyhedral linkage defined by each intermediate that we term conformational diffusion. The combinatorial configuration space of the model is computed for the Platonic, Archimedean, and Catalan solids of up to 30 faces, and several novel enumerative results are generated. These represent the most exhaustive computations of this nature to date. We further extend the building game to include geometric information. The combinatorial structure of each intermediate yields a systems of constraints specifying a polyhedral linkage and its moduli space. We use a random walk to simulate a reflected Brownian motion in each moduli space. Empirical statistics of the random walk may be used to define the rates of transition for a Markov process modeling the process of self-assembly.     

LESSER KNOWN MIRACLES OF BURGERS EQUATION

This article is a short introduction to the surprising appearance of Burgers equation in some basic probabilistic models.