Inertial Attached Length of an Orifice at High Sound Pressure Levels

Effect of sound pressure level on acoustic impedance of an orifice in a baffle is investigated based on the measurements performed in an impedance tube by the two-microphone method. Dependences of imaginary and real parts of impedance on the orifice diameter are obtained in nonlinear conditions. Special attention is paid to the attached length (the end correction) of the orifice. Dependence of the attached length of an orifice on the oscillating velocity in it is approximated by analytic functions.     

Macrokinetics of carbonaceous feedstock pyrolysis in a tubular reactor of variable cross section

A macrokinetic model of carbonaceous feedstock pyrolysis in a tubular reactor of variable cross section was constructed. It was shown that, to intensify the pyrolysis in such a tubular reactor, its diameter should vary depending on the viscosity of the reaction products.     

Efficient implementation of the analytic second derivatives of Hartree–Fock and hybrid DFT energies: a detailed analysis of different approximations

In this paper, various implementations of the analytic Hartree–Fock and hybrid density functional energy second derivatives are studied. An approximation-free four-centre implementation is presented, and its accuracy is rigorously analysed in terms of self-consistent field (SCF), coupled-perturbed SCF (CP-SCF) convergence and prescreening criteria. The CP-SCF residual norm convergence threshold turns out to be the most important of these. Final choices of convergence thresholds are made such that an accuracy of the vibrational frequencies of better than 5 cm^?1 compared to the numerical noise-free results is obtained, even for the highly sensitive low frequencies (<100–200 cm^?1). The effects of the choice of numerical grid for density functional exchange–correlation integrations are studied and various weight derivative schemes are analysed in detail. In the second step of the work, approximations are introduced in order to speed up the computation without compromising its accuracy. To this end, the accuracy and efficiency of the resolution of identity approximation for the Coulomb terms and the semi-numerical chain of spheres approximation to the exchange terms are carefully analysed. It is shown that the largest performance improvements are realised if either Hartree–Fock exchange is absent (pure density functionals) and otherwise, if the exchange terms in the CP-SCF step of the calculation are approximated by the COSX method in conjunction with a small integration grid. Default values for all the involved truncation parameters are suggested. For vancomycine (176 atoms and 3593 basis functions), the RIJCOSX Hessian calculation with the B3LYP functional and the def2-TZVP basis set takes ～3 days using 16 Intel® Xeon® 2.60GHz processors with the COSX algorithm having a net parallelisation scaling of 11.9 which is at least ～20 times faster than the calculation without the RIJCOSX approximation.     

STRUCTURE AND CATALYTIC PROPERTIES OF PALLADIUM(II) (ACETYLACETONATO- κ2O,O′)BIS(TRIS(DIETHYLAMINO)PHOSPHINE) TETRAFLUOROBORATE

Journal of Structural Chemistry - The structure of complex [Pd(acac){P(NEt2)3}2]BF4 (I) is determined by XRD. In the crystal structure of I, the coordination sphere of palladium is characterized by...     

Nitride Spinel: An Ultraincompressible High‐Pressure Form of BeP2N4

Owing to its outstanding elastic properties, the nitride spinel γ‐Si₃N₄ is of considered interest for materials scientists and chemists. DFT calculations suggest that Si₃N₄‐analog beryllium phosphorus nitride BeP₂N₄ adopts the spinel structure at elevated pressures as well and shows outstanding elastic properties. Herein, we investigate phenakite‐type BeP₂N₄ by single‐crystal synchrotron X‐ray diffraction and report the phase transition into the spinel‐type phase at 47 GPa and 1800 K in a laser‐heated diamond anvil cell. The structure of spinel‐type BeP₂N₄ was refined from pressure‐dependent in situ synchrotron powder X‐ray diffraction measurements down to ambient pressure, which proves spinel‐type BeP₂N₄ a quenchable and metastable phase at ambient conditions. Its isothermal bulk modulus was determined to 325(8) GPa from equation of state, which indicates that spinel‐type BeP₂N₄ is an ultraincompressible material.     

Nonlinear base models of macrokinetics

The conception of base macrokinetic models of processes taking place on the catalyst surface has been developed by analysis of nonlinear distributed models. This conception implies a parametric analysis of the simplest models allowing multiple steady states, self-oscillations, and the existence of unsteady-state dissipative structures.     

Thermodynamic study on the composition of the gas phase over melts of an aluminum-scandium system

The vapor pressure of the gas phase components over Al-Sc melts was studied. The temperatures and the variation of the enthalpy upon “melt-gas” phase transformations were determined. The simulation was performed in an initial medium of argon at a total pressure of 10⁵ Pa and temperatures T = 1873−4000 K.