Dissipative terms of thermal nature in the theory of an ideal monoatomic superfluid

A dissipative model of helium II was built up in previous works, using a 13-field extended thermodynamic theory formulated by Liu and Müller. In this work a generalization of such model is presented, where an extended thermodynamics with 14 fields due to Kremer is used. It is shown that the fourteenth field is able to account for the experimental data concerning the second sound attenuation. Further, the proposed theory is able to explain the Osborne experiment. Finally, a comparison with the two-fluid model is performed, emphasizing the different ways in which the dissipative phenomena are explained by the two theories.     

On trifactorized soluble minimax groups

This research was done while the last two authors were visitors at the University of Mainz. They are grateful to the Department of Mathematics for its excellent hospitality.     

Registering the Amica electronic structure code in the extensible computational chemistry environment

We describe the integration and use of the Amica software package ("Atoms & Molecules In Chemical Accuracy") within the Extensible Computational Chemistry Environment (Ecce). Amica is capable of accurately solving the electronic Schrodinger equation of small atoms and molecules using terms that are linear in the interelectronic distances, r(12), on multireference level of theory, but it requires expert knowledge to configure and execute its algorithms. Ecce is a comprehensive suite of tools that support the computational chemistry research processes of computation setup, execution, and analysis through a convenient graphical user interface. Additionally, Ecce was architected with mechanisms to integrate alternative electronic structure codes. The successful integration of Amica within Ecce validates the architecture of the latter and brings the high-accuracy capabilities of Amica to a wider audience.     

Direct dynamics study of ultrafast vibrational energy relaxation in ice Ih

Car-Parrinello molecular dynamics (CPMD) and a previously developed wave packet model are used to study ultrafast relaxation in water clusters. Water clusters of 15 water molecules are used to represent ice Ih. The relaxation is studied by exciting a symmetric or an asymmetric stretch mode of the central water molecule. The CPMD results suggest that relaxation occurs within 100 fs. This is in agreement with experimental work by Woutersen and Bakker and the earlier wave packet calculations. The CPMD results further indicate that the excitation energy is transferred both intramolecularly and intermolecularly on roughly the same time scale. The intramolecular energy transfer occurs predominantly between the symmetric and asymmetric modes while the bend mode is largely left unexcited on the short time scale studied here.     

Characterization of interactions in aqueous solutions of hydroxyethylcellulose and its hydrophobically modified analogue in the presence of a cyclodextrin derivative

The formation of associative networks in semidilute aqueous solutions of hydrophobically modified hydroxyethylcellulose (HM-HEC) is dependent on intermolecular hydrophobic interactions. Addition of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) monomers to the system provides decoupling of these associations via inclusion complex formation with the polymer hydrophobic tails. Results from viscosity, polymer NMR self-diffusion, and dynamic light scattering (DLS) measurements show that the hydrophobic interactions in HM-HEC solutions are effectively suppressed when the level of HP-beta-CD addition increases. Small-angle neutron scattering (SANS) results reveal that the large-scale association complexes in HM-HEC solutions are strongly diminished when the concentration of HP-beta-CD rises. The time correlation data obtained from the DLS experiments unveiled the existence of two relaxation modes: one single exponential at short times followed by a stretched exponential at longer times. The fast mode is always diffusive, whereas the slow mode exhibits progressively stronger wavevector dependence as the intensity of the hydrophobic interactions increases. This feature, as well as the accompanying drop of the stretched exponential beta as the HP-beta-CD concentration decreases, is attributed to enhanced hydrophobic interactions and can be well rationalized in the framework of the coupling model of Ngai.     

Absorption cross sections of formaldehyde at wavelengths from 300 to 340 nm at 294 and 245 K

Absorption cross sections for the A1A2-X1A1 electronic transition of formaldehyde have been measured by ultraviolet (UV) laser absorption spectroscopy in the tropospherically significant wavelength range 300-340 nm, over which HCHO is photochemically active. Absorption cross sections are reported at two temperatures, 294 and 245 K and at a spectral resolution of 0.0035 nm (0.35 cm-1). At this resolution, greater peak absorption cross sections are obtained for many of the sharp spectral features than were previously reported. To simulate atmospheric conditions in the troposphere, the effects of adding a pressure of nitrogen of up to 500 Torr and of reduced sample temperature were investigated. The overall magnitudes of peak absorption cross sections are largely unaffected by the added pressure of nitrogen, but a modest degree of pressure broadening (0.2-0.3 cm-1 atm-1) is evident in the line shapes. Computer simulations of spectra have been optimized by comparison with wavelength-dependent formaldehyde absorption cross sections for each major vibronic band in the chosen wavelength range. Experimental and computer simulated spectra at 294 and 245 K are compared to test the reliability of the computer simulations for quantification of the effects of temperature on absorption cross sections. All experimental absorption cross section data and tables of input parameters for spectral simulations are available as Supporting Information.     

Selective enzymatic reduction of aldehydes

Highly selective enzymatic reductions of aldehydes to the corresponding alcohols was performed using an E. coli JM109 whole cell biocatalyst. A selective enzymatic method for the reduction of aldehydes could provide an eco-compatible alternative to chemical methods. The simplicity, fairly wide scope and the very high observed chemoselectivity of this approach are its most unique features.     

Autocorrelation function formulations and the turbulence dissipation rate: Application to dispersion models

The classical statistical diffusion theory and the binomial autocorrelation function are used to obtain a new formulation for the turbulence dissipation rate ε. The approach employs the Maclaurin series expansion of a logarithm function contained in the dispersion parameter formulation. The numerical coefficient of this new relation for ε is 100% larger than the numerical coefficient of the classical relation derived from the exponential autocorrelation function. A similar approach shows that the dispersion parameter obtained from the even exponential autocorrelation function does not result in a relation for ε and, therefore, is not suitable for application in dispersion models. In addition, a statistical comparison to experimental ground-level concentration data demonstrates that this newly derived relation for ε as well as other formulations for the turbulence dissipation rate are suitable for application in Lagrangian stochastic dispersion models. Therefore, the analysis shows that there is an uncertainty regarding the turbulence dissipation rate function form and the autocorrelation function form.