A new method for tieline calculations in binary fluid systems

We describe a method to determine tielines for a mixture with a given volume V_t and a given mole fraction x_t at fixed temperature, which is based on the orientation of the tangent plane to the Helmholtz free energy surface. The method works equally well for gas-liquid separation as for liquid-liquid separation. The method is based on a rotation in coordinate space followed by a rotation in function space which establishes the correct direction and the end points of the tieline. The mathematics is described and the general outline of a computer program to implement the method is given. This is followed by an application to a special form of the van der Waals equation, which describes the influence of chain-molecules as proposed by Tompa. The example given shows a three phase separation and the influence of the chain-length thereupon.     

On polyhedral extension of some LP theorems

McLinden (Mathematical Programming 24 (1982) 162–176) has extended theorems of Tucker (1956) and Williams (1970) on the complementarity behaviour of feasible and optimal solutions to a pair of canonical linear programs to proper convex polyhedral functions. He achieved this by heavily using the well-developed machinery of convex analysis. In this note, we prove most of his results mainly using linear programming theory.     

Reactions with heterocyclic diazonium salts. Synthesis of several new azolylhydrazones

Several new stable azolylhydrazones could be synthesized via coupling of diazotised cycliuc amidines with active methylene reagents. The obtained compounds were utilised for synthesis of several, otherwise not readily accessible fused azoles.     

A Note on Shadow Prices in Linear Programming

Using convex analysis and a characterization of the entire family of optimal solutions to an L.P., we show that in order to obtain shadow prices, one has to solve a much smaller L.P. derived from any optimal tableau. We then show that positive as well as negative shadow prices for any constraint or for any combination of constraints can easily be computed by parametric linear programming. Some examples exhibiting the method are also included.     

Distribution of eigenvalues for the discontinuous boundary-value problem with functional-manypoint conditions

In this study, we investigate the boundary-value problem with eigenvalue parameter generated by the differential equation with discontinuous coefficients and boundary conditions which contains not only endpoints of the considered interval, but also a point of discontinuity, a finite number of internal points and abstract linear functionals. So our problem is not a pure boundary-value one. We single out a class of linear functionals and find simple algebraic conditions on the coefficients which guarantee the existence of an infinite number of eigenvalues. Also, the asymptotic formulas for the eigenvalues are found. The results obtained in this paper are new, even in the case of boundary conditions either without internal points or without linear functionals.     

Deoxygenation and X-ray photoelectron studies on some quinoxalines and their N-oxides

Deoxygenation results of some quinoxaline dioxides with phosphorous trichloride are presented and compared with previous deoxygenations with other reagents. Differentiation between isomeric quinoxaline oxides using X-ray photoelectron spectroscopy is also discussed.     

Partition of supercritical n-pentane into SE-54 and SE-30 stationary phases in capillary supercritical fluid chromatography

Summary The mass spectrometric tracer pulse (MSTP) chromatography method was used to measure the amount of supercritical n-pentane dissolved or adsorbed into SE-54 and SE-30 capillary columns. Partition data were measured above the critical point of n-pentane at temperatures from 200 ° to 300 °C and pressures between 35.04 and 54.42 atm. The data obtained provide evidence for mobile fluid solubility or adsorption into the stationary phase under the conditions of supercritical fluid chromatography (SFC). At 220 °C, solubility and/or adsorption of supercritical n-pentane decreases by increasing the pressure and reaches a minimum at approximately 45.00 atm. The effect of mobile-fluid pressure on its solubility or adsorption becomes limited at temperatures over 260 °C. This study demonstrates the unique experimental capabilities of the MSTPC method for quantitative measurement of the physico-chemical interaction of the complex multicomponent system encountered in SFC which is not possible by any other technique. An innovative instrumental design for modification of GC/MS systems for SFC, GC/MS operation is also described.

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Verteilung von superkritischem n-Pentan in den stationären Phasen SE-54 und SE-30 bei der Capillar-Chromatographie mit superkritischen fluiden Phasen

     

Near-field performance analysis of locally-conformal perfectly matched absorbers via Monte Carlo simulations

In the numerical solution of some boundary value problems by the finite element method (FEM), the unbounded domain must be truncated by an artificial absorbing boundary or layer to have a bounded computational domain. The perfectly matched layer (PML) approach is based on the truncation of the computational domain by a reflectionless artificial layer which absorbs outgoing waves regardless of their frequency and angle of incidence. In this paper, we present the near-field numerical performance analysis of our new PML approach, which we call as locally-conformal PML, using Monte Carlo simulations. The locally-conformal PML method is an easily implementable conformal PML implementation, to the problem of mesh truncation in the FEM. The most distinguished feature of the method is its simplicity and flexibility to design conformal PMLs over challenging geometries, especially those with curvature discontinuities, in a straightforward way without using artificial absorbers. The method is based on a special complex coordinate transformation which is ‘locally-defined’ for each point inside the PML region. The method can be implemented in an existing FEM software by just replacing the nodal coordinates inside the PML region by their complex counterparts obtained via complex coordinate transformation. We first introduce the analytical derivation of the locally-conformal PML method for the FEM solution of the two-dimensional scalar Helmholtz equation arising in the mathematical modeling of various steady-state (or, time-harmonic) wave phenomena. Then, we carry out its numerical performance analysis by means of some Monte Carlo simulations which consider both the problem of constructing the two-dimensional Green’s function, and some specific cases of electromagnetic scattering.     

Temperature dependence of transport characteristics of wurtzite GaN epilayers

We report electrical transport properties of intentionally and unintentionally doped wurtzite GaN epilayers within the temperature range of 3K up to 340 K. Specifically, temperature dependence of the carrier concentration, mobility and resistivity are investigated. Obtained data could only be explained on the basis of two-band model, namely, high mobility conduction band and low mobility impurity band. The threshold doping concentration for the dominance of the conduction band electrons is estimated to be about 10¹⁸ cm^–3.