Additive-subtractive phase-modulated speckle interferometry: Fringe visibility under partial decorrelation

Additive-subtractive phase modulated speckle interferometry (ASPMSI) is a technique that minimizes the susceptibility of speckle methods to environmental noise while providing fringes of good visibility. The method requires the acquisition of two consecutive video frames of additive-speckle images of the same two deformed states of an object at a rapid enough rate such that ambient noise is not a problem. The additive-speckle images as expected are of very poor visibility due to the presence of the self-interference term. An interframe phase-modulation is introduced and the two additive-speckle images are digitally subtracted to improve the fringe visibility by removing the self-interference term. The ASPM-SI method works with in-plane and out-of-plane deformation sensitive ESPI as well as with displacement-gradient sensitive speckle-shearing interferometry. It is shown that the ASPM-SI scheme has higher visibility than conventional additive-SI and performs consistently better than subtractive-SI schemes in the presence of partial interframe speckle decorrelating optical noise. Furthermore, it is shown that the fringe visibility of the out-of-plane displacement sensitive interferometer which uses a protected reference beam separate from the object beam can be made to be essentially unity even at complete interframe decorrelation.     

Modeling high-pressure densities at wide temperature range with volume scaling: Cyclohexane + n-hexadecane mixtures

High-pressure density data for cyclohexane + n-hexadecane mixtures at a wide temperature range was modeled with several classical equations of state (EOS) and correlative models. A modification for softening the co-volume and another for a volume scaling of the Peng–Robinson EOS (VS-PR) were proposed. The VS-PR model is able to correlate the pure component experimental data employing only five adjustable parameters, with root-mean-square deviation (RMSD) between calculated and experimental densities essentially within the experimental error. This result is superior to widely used approaches, i.e., a six parameter Tait model and six parameter volume translations (temperature and pressure dependent) for Peng–Robinson and Patel–Teja EOS. The VS-PR model also represents well the isobaric thermal expansion and the isothermal compressibility coefficients of the pure cyclohexane, a small naphthenic substance as well as a long chain n-alkane hydrocarbon, n-hexadecane. When modeling the mixture data, the use of VS-PR model of pure components along with the Redlich–Kister expansion, truncated at the first term, the density was correlated within a RMSD only 60% greater than the experimental error. The proposed model is able to accurately represent all the tested mixture data with a relatively small number of parameters.     

In situ UV-visible spectroelectrochemical studies on the copolymerization of diphenylamine with ortho-methoxy aniline

UV-visible spectroelectrochemical studies on copolymerization of diphenylamine (DPA) with ortho-methoxy aniline (OMA) were carried out for different feed ratios of DPA and OMA using indium tin oxide (ITO)-coated glass as working electrode. The UV-visible spectra show clear dependencies on the molar feed composition of DPA or OMA used in electropolymerization. Derivative cyclic voltabsorptogram (DCVA) was deduced at the wavelengths corresponding to the absorption by the intermediate species and used to confirm the intermediates generated during the electropolymerization. The composition of DPA and OMA in the copolymer for the copolymers synthesized with different molar feed ratios of DPA and OMA was determined by UV-visible spectroscopy. Reactivity ratios of DPA and OMA were deduced by using Fineman-Ross and Kelen-Tudos methods and correlated with spectroelectrochemical results.     

Ab initio scf and CI study of the ground and excited states of the HN2 radical

Non-empirical SCF and CI calculations are reported for the HN₂, free radical in various low-lying electronic states. The nature of the angular and N-N and N-H stretching potential curves of each of these species is investigated, including a study of the dissociative behavior of such states. The ground state is found to be only very slightly bound with respect to NH stretch, in contrast to what is observed for isoelectronic HCO, The vertical electronic spectrum of HN₂, appears to be marked by a single long wavelength transition (1.95 eV) from the bent (124°) ‘A’ ground state to the linear ²Π excited species, but at least four other intra-valence and an additional n → 3s Rydberg species are indicated in the 5.5–8.0 eV absorbing region.     

An analysis of the complex molecular orbitals method

Numerical results for the ground state of the HN ₂ ⁺ and HCO⁺ molecular ions at their near equilibrium geometry, obtained by the complex molecular orbitals (CMO) method in the extended basis set, are reported. The CMO wavefunction of the HN ₂ ⁺ ion is compared with the CI wavefunction obtained in the same basis set. This reveals the nature of approximations inherent in the CMO method. A peculiar feature of the occupation numbers of the CMO natural orbitals is also explained.Alexander von Humboldt Fellow. On leave from the Institute Rudjer Bokovi, Zagreb, Croatia, Yugoslavia.     

Orientational dynamics of anthracene in a cyclodextrin functionalized layered solid

Cyclodextrin cavities have been intercalated in a layered metal hydroxide to create hydrophobic nanopockets within the galleries of the layered solid. Anthracene molecules have been included in the anchored cavities by partitioning from a polar solvent. The excitation-emission fluorescence spectra of the included anthracene show a total absence of Stokes shift. The orientational dynamics of the isolated, solvent-free anthracene molecules in the anchored cyclodextrin cavities have been probed by fluorescence anisotropy decay measurements. The results have been compared with those for anthracene included in cyclodextrin cavities in aqueous solutions.     

Adsorption of n-hexane in zeolite-5A: a temperature-programmed desorption and IR-spectroscopic study

The adsorption and desorption of n-hexane over Zeolite-5A has been investigated as a function of loading using simultaneous Fourier transform infrared (FTIR)-temperature-programmed desorption (TPD) measurements. The TPD profiles show a second peak developing at lower temperatures when loading exceeds 16 hexane molecules per Zeolite-5A unit cell or two molecules per alpha-cavity of the Zeolite-5A structure. The infrared spectra rule out two types of adsorption sites as the origin of the two peaks in the TPD. Changes in the conformation of the adsorbed hexane as a function of loading and temperature were followed by monitoring the position of the methylene stretching modes in the infrared spectra. With increasing loading, the adsorbed hexane adopts a stretched trans conformation. These changes occur at loading levels below 12 hexane molecules per Zeolite-5A unit cell. No change is observed above this loading, ruling out any conformational change at loadings where the second peak is seen in the TPD. The second peak in the TPD arises, therefore, from a combination of steric repulsion and loss of translational entropy.     

Theoretical study of the electronic spectrum of diimide by AB initio methods

A series of ab initio calculations is reported for the ground and low-lying valence and Rydberg states of diimide N₂H₂. Symmetric bending potential curves for both the cis and trans forms of this system have been obtained at the SCF level of treatment. In addition Cl calculations have been carried out for the trans-diimide ground state equilibrium nuclear conformation, using a configuration selection procedure described elsewhere; an associated energy extrapolation scheme is also employed which enables the effective solution of secular equations with orders of up to 40000. The ensuing Cl wavefunctions are interpreted in the discussion and the corresponding calculated energy differences between the various electronic states are compared with experimental transition energy results for both diimide and for related systems such as trans-azomethane. A more detailed analysis of the observed absorption bands in the ¹B_g-X¹A_g transition in N₂H₂ is also given, making use of calculated potential curve data as well as the pertinent Cl vertical energy difference. The dipole-forbiddenness of the excitation process is thereupon concluded to result in a distinct non-verticality for this electronic band system, causing its absorption maximum to occur at a position some 0.6 eV to the blue of the so-called vertical transition, i.e., that for which maximum vibrational overlap is obtained.     

LiNi<Subscript>0.8</Subscript>Co<Subscript>0.2−x</Subscript>Ti<Subscript>x</Subscript>O<Subscript>2</Subscript> nanoparticles: synthesis,structure, and evaluation of electrochemical properties for lithium ion cell application

Layered Ti-doped lithiated nickel cobaltate, LiNi_0.8Co_{0.2 − x}Ti_xO₂ (where x = 0.01, 0.03, and 0.05) nanopowders were prepared by wet-chemistry technique. The structural properties of synthesized materials were characterized by X-ray diffraction (XRD) and thermo-gravimetric/differential thermal analysis (TG/DTA). The morphological changes brought about by the changes in composition of LiNi_0.8Co_{0.2 − x}Ti_xO₂ particles were examined through surface examination techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. Electrochemical studies were carried out using 2016-type coin cell in the voltage range of 3.0–4.5 V (vs carbon) using 1 M LiClO₄ in ethylene carbonate and diethyl carbonate as the electrolyte. Among the various concentrations of Ti-doped lithiated nickel cobaltate materials, C/LiNi_0.8Co_0.17Ti_0.03O₂ cell gives stable charge–discharge features.