Nice Correlations Research Articles

Direct Irradiation of Phenol and Para-Substituted Phenols with a Laser Pulse (266 nm) in Homogeneous and Micro-heterogeneous Media. A Time-Resolved Spectroscopy Study

Direct irradiation of para-substituted phenols under N2 atmosphere in homogeneous (cyclohexane, acetonitrile, and methanol) and micellar (SDS) solution was investigated by means of time-resolved spectroscopy. After a laser pulse (266 nm), two transient species were formed, viz. the para-substituted phenol radical-cations and the corresponding phenoxy radicals. The radical-cations showed a broad absorption band located between 390 and 460 nm, while the phenoxy radicals showed two characteristic bands centered at 320 nm and 400-410 nm. The deprotonation rate constant of radical-cations (kH) of 105 s-1 and the reaction rate constant of the phenoxy radicals (kR) in the order of 109-1010 M-1·s-1 have been derived. The kH rate constants gave good linear Hammett correlation with positive slope indicating that electron-withdrawing substituents enhance the radical-cation acidity. The binding constants (Kb) of the para-substituted phenols with the surfactant were also measured, and NOESY experiments showed that phenols were located in the hydrophobic core of the micelle. Finally, computational calculations provided the predicted absorption spectra of the transients and nice linear correlations were obtained between the theoretical and experimental energy of the lower absorption band of these species.

Stability boundary analysis of highly flexible aircraft with control saturation and structural flexibility

In this work, a method has been presented to analyze the influence of control saturation and structural flexibility on the stable radius of highly flexible aircraft. A dynamic model of aircraft is constructed followed by the analysis of kinetic characteristics. In this paper, the closed-loop stability boundary of highly flexible aircraft with open-loop instability is studied. The amplitude limit and bandwidth limit of the control signal are considered in the closed-loop stability boundary calculation. Our analysis shows that the boundary is related to the left eigenvector corresponding to the unstable poles and the amplitude constraint of the control signals. Stability of the boundary of feedback control system further reduces the limitation of the bandwidth of actuators. Focused on the phugoid instability of highly flexible aircraft, computational formulation of the closed-loop stable boundary is achieved. The Monte Carlo analysis has been employed to validate the stable region, under the LQR controller. Both the theory and simulations have nice correlations with each other which verify the stability of the closed-loop system, restricted by the open-loop system, and the influence of control signal bandwidth constraints.

Study on Quantitative Correlations between the Ageing Condition of Transformer Cellulose Insulation and the Large Time Constant Obtained from the Extended Debye Model

Polarization-depolarization current (PDC) measurements are now being used as a diagnosis tool to predict the ageing condition of transformer oil-paper insulation. Unfortunately, it is somewhat difficult to obtain the ageing condition of transformer cellulose insulation using the PDC technique due to the variation in transformer insulation geometry. In this literature, to quantify the ageing condition of transformer cellulose insulation using the PDC technique, we firstly designed a series of experiments under controlled laboratory conditions, and then obtained the branch parameters of an extended Debye model using the technique of curve fitting the PDC data. Finally, the ageing effect and water effect on the parameters of large time constant branches were systematically investigated. In the present paper, it is observed that there is a good exponential correlation between large time constants and degree of polymerization (DP). Therefore, the authors believe that the large time constants may be regard as a sensitive ageing indicator and the nice correlations might be utilized for the quantitative assessment of ageing condition in transformer cellulose insulation in the future due to the geometry independence of large time constants. In addition, it is found that the water in cellulose pressboards has a predominant effect on large time constants.

On the origin of donor O-H bond weakening in phenol-water complexes.

Matrix isolation infrared spectroscopy has been used to investigate intermolecular interactions in a series of binary O-H⋯O hydrogen bonded phenol-water complexes where water is the common acceptor. The interaction at the binding site has been tuned by incorporating multiple fluorine substitutions at different aromatic ring sites of the phenol moiety. The spectral effects for the aforesaid chemical changes are manifested in the infrared spectra of the complexes as systematic increase in spectral shift of the phenolic O-H stretching fundamental (ΔνO-H). While νO-H bands of the monomers of all the fluorophenols appear within a very narrow frequency range, the increase in ΔνO-H of the complexes from phenol to pentafluorophenol is very large, nearly 90%. The observed values of ΔνO-H do not show a linear correlation with the total binding energies (ΔEb) of the complexes, expected according to Badger-Bauer rule. However, in the same ΔνO-H vs ΔEb plot, nice linear correlations are revealed if the complexes of ortho-fluorophenols are treated separately from their meta/para-substituted analogues. The observations imply that in spite of having the same binding site (O-H⋯O) and the same chemical identities (phenolic), the complexes of ortho and non-ortho fluorophenols do not belong, from the viewpoint of detailed molecular interactions, to a homologous series. Linear correlations of ΔνO-H are, however, observed with respect to the electrostatic component of ΔEb as well as the quantum mechanical charge transfer interaction energy (ECT). From quantitative viewpoint, the latter correlation along with the associated electronic structure parameters appears more satisfactory. It has also been noted that the observed ΔνO-H values of the complexes display a linear relationship with the aqueous phase pKa values of the respective phenol derivatives.

The dual role of halogen, chalcogen, and pnictogen atoms as Lewis acid and base: Triangular XBr:SHX:PH2X complexes (X = F, Cl, Br, CN, NC, OH, NH2, and OCH3)

Using ab initio calculations, we have investigated the possibility of formation of triangular XBr:SHX:PH2X complexes, where X5 F, Cl, Br, CN, NC, OH, NH2, and OCH3. These complexes are formed through the interaction of a positive electrostatic potential region (r-hole) on a molecule with the negative region in another one. The results show that the combined halogen, chalcogen, and pnictogen interactions can give rise to stable cyclic structures. The interaction energies of these complexes span over a wide range, from 23.55 to 224.93 kcal/mol. Nice quadratic correlations are found between the interaction energies and binding distances in the trimers. To understand the nature of the interactions in these complexes, molecular electrostatic potential and quantum theory of atoms in molecule analyses are performed. VC 2015 Wiley Periodicals, Inc.

Synthesis, characterization and density functional theory study of some new 2-anilinothiazoles

We report here a comparative theoretical and experimental study of anilinothiazoles. The anilinothiazoles are synthesized by acid catalyzed condensation of N-phenylthioureas and 2-chloro-1,1-dimethoxyethane. Substituted anilines were employed to introduce substitution in 2-anilinothiazoles. The experimental geometric and spectroscopic properties of the anilinothiazoles are compared with the theoretically calculated ones. The model developed here comprises of geometry optimization at B3LYP method of DFT at 6-31+G(d) basis set. The optimized geometric parameters of anilinothiazoles show nice correlations with values obtained from X-ray crystal structure. Differences of up to 0.02Å in bond length and 1.0° in bond angles are observed except SC2N6 and C7N6C2 where this difference is 1.77° and 6.01°, respectively. The vibrational spectra are calibrated with a common scaling factor of 0.9613 and show nice correlations with the experimental IR spectra. The UV–Vis spectra calculated at 190–450nm range show 20–25nm difference from the experimental spectra. The consistent difference may be attributed to the condensed phase nature of anilinothiazoles however the theoretical spectra are for single molecules. In addition HOMO, LUMO and the associated band gaps are also calculated and depicted.

Evidences to the pulse like origin of double spicules based on Hinode/SOT observations

We analyze the time series of H$\alpha$ line obtained from Hinode/SOT on the solar limb. The wavelet analysis shows that there are nice correlations between dynamical properties of the two parts of a double spicule. The dominant periods for height variations are estimated ~90 and ~180 s. The length of two parts of the spicule oscillates with the period of around ~180 s. The mean distance between two parts of the spicule has a periodical treatment with the period of ~90 s. Our results show that the strong pulses may lead to the quasi periodic rising of chromospheric plasma into the lower corona in the form of spicules. The periodicity may result from the nonlinear wake behind the pulse in the stratified atmosphere.

Theoretical study of phenyl-substituted indacenodithiophene copolymers for high performance organic photovoltaics

The theoretical estimation of energy levels and energy gaps of conjugated polymers for organic photovoltaics (OPVs) represents in principle a useful tool for the prescreening of new donor systems as a suitable pair for the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM). In this study, ten tetraphenyl-substituted indacenodithiophene (IDT) copolymers (eight in the form of donor-acceptor), whose energy gaps vary in the range of 1.48-2.11 eV have been selected and their highest occupied molecular orbitals (HOMOs), lowest unoccupied molecular orbitals (LUMOs), and gap energies have been calculated by applying density functional theory (DFT) and/or time-dependent density functional theory (TD-DFT) methods. In spite of the examined molecular structure variety, nice correlations (theoretical models) between experimental and theoretical electronic parameters were found. It is shown that the theoretical band gap estimated by the TD-DFT using dimer model compounds and DFT using tetramer model compounds provide in good agreement the optical band gap of these polymers. Finally, the optimum theoretical limits of the LUMO offset between the fullerene and the IDT tetramer model compounds, for which high performance OPVs (efficiency > 6%) are obtained, is presented for the first time.

Irreducible Divisor Graphs and Factorization Properties of Domains

This article examines the connections between the factorization properties of a domain, e.g., unique factorization domain (UFD), finite factorization domain (FFD), and the domain's irreducible divisor graphs. In particular, we show that although there are some nice correlations between the properties of the domain D and the set of irreducible divisor graphs {G(x): x ∈ D* \\ U(D)} when D is an FFD, it is very unlikely that any information about the domain D can be gleaned from the collection {G(x): x ∈ D* \\ U(D)} when D is not an FFD. We also introduce an alternate irreducible divisor graph called the compressed irreducible divisor graph and study some of its properties.

Comparison between theoretical and experimental electronic properties of some popular donor polymers for bulk-heterojunction solar cells

The theoretical estimation of energy levels and energy gaps of conjugated polymers for polymer solar cells represents in principle an useful tool for an a priori screening of new donor systems. Fourteen polymers, whose energy gaps vary in the range 1.2–3.1 eV have been selected and their HOMO, LUMO and gap energies have been calculated by applying Density Functional Theory methods. In spite of the variety of the examined molecular structures, nice correlations between theoretical and experimental electronic parameters were found. In particular, optical gaps and, to a lesser extent, electrochemical gap very well correlate with theoretical gaps, while for the other parameters (oxidation and reduction potentials) the general trend is reproduced. It is shown that, in general, the theoretical energies of the base repeating units have values close to the experimental energies, but the linear fittings are better when the theoretical data of much longer chains are considered: infinitely long chains must be used to predict the optical gaps, while long oligomers are more appropriate to estimate the electrochemical properties. Criteria and relationships for the prediction of energy data from theoretical ones are provided.

A Loosely Synchronous-Coded OFDM System for Power-Line Communications in Home Networks

High-speed data communication is critical for home networks to support the increasing needs of online multimedia entertainment. Power-line communication (PLC) presents a 'no new wires' solution for home networks. However, power line is a troublesome and noisy platform for home networks. And the traditional approach with PLC is interference-limited and has a small bandwidth. In this paper we propose a new scheme of orthogonal frequency-division multiplexing (OFDM) to provide better noise-limited PLC networks. This schema is based on loosely synchronous (LS) codes with very nice correlations. Construction criteria of LS codes used in the proposed system are provided and discussed. The capacity properties and spectral efficiency of LS coded OFDM systems over PLC channels are also studied in this paper. We show that the proposed LS coded OFDM can efficiently achieve the diversity provided by power line channels. Such a schema can be employed in PLC to increase data throughput, system capacity and spectral efficiency in home networks

Évaluation de l'effet électroattracteur du motif 4-nitrobenzofurazanyle : ionisation de 7-anilino 4-nitrobenzofurazanes

The ionization of a series of 7-(4′-X anilino) 4-nitrobenzofurazans (4H) (X = NO2, CN, CO2Me, F, H, Me, OMe) to give the conjugate amide anions 4− has been studied by 1H and 13C NMR in Me2SO-d6. Concomitantly, their acidity (pKa) has been measured spectrophotometrically in a H2O–Me2SO mixture with a molar fraction [Formula: see text] Although the measured pKa values for the whole series of compounds 4H lie in a relatively narrow range (6.40, X = NO2/7.98, X = OMe), they reveal that each derivative is about 3 times more acidic than the similarly X-substituted 2,4,6-trinitrodiphenylamines. These results, together with an analysis of substituent effects on the proton and carbon chemical shifts [Formula: see text] and the related deprotonation parameters (Δδ), which are specially significant for H6, C4, C6, and C7, emphasize the very strong electron-withdrawing character of the 4-nitrobenzofurazanyl moiety. In addition, the observation of nice linear correlations of the type [Formula: see text] has enabled us to control and sometimes to firmly assign the various chemical shifts. Keywords: 7-anilino 4-nitrobenzofurazans, acidities, 1H and 13C NMR deprotonation shifts, water – dimethyl sulfoxide mixtures.

General discussion

Voigt: I would like to make one general critical remark. Almost all papers about narrow-band photometry have given nice correlations between some narrow-band parameters and other properties of the stars to prove the value for classification, but one hardly finds any paper where these parameters are used to classify new faint stars not classified hitherto. Therefore my question: when will narrow-band photometry have been improved so far that observers can apply it to new material which should be of course the final purpose?