Vaporization enthalpies of imidazolium based ionic liquids: dependence on alkyl chain length

Vaporization enthalpies of a series of ten 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids (ILs) [C(n) mim][NTf(2) ] with alkyl chain lengths of n=2, 3, 4, 6, 8, 10, 12, 14, 16, and 18 are determined by using a recently developed quartz crystal microbalance method. Due to the high sensitivity of the microbalance vapor studies can be extended to temperatures 60-100 K lower than those available with other methods. The results reveal a remarkably linear dependence of the vaporization enthalpies on the chain length at the reference temperature of 298 K.     

Pressure and temperature dependence of the excess enthalpy of alkylchloride/alkane mixtures

There exist only few experimental data of the excess enthalpy of liquid mixtures at high pressure in literature. In this work some recent experimental results of the excess enthalpy H^E for alkylchloride/alkane mixtures are reported measured at different pressures and temperatures by using a high pressure flow calorimeter. H^E shows a relatively weak dependence on pressure compared with other polar/unpolar systems such as alcohol/alkane mixtures (ref.1).     

Differential non-destructive image current detection in a fourier transform quadrupole ion trap

Dual-detector differential non-destructive Fourier transform detection in a quadrupole ion trap is shown to improve signal intensity and reduce noise compared with spectra recorded using a single detector. A larger area detector in each end-cap electrode is machined to fit its hyperbolic shape and so minimize field imperfections on the z-axis. Argon, acetophenone and bromobenzene spectra were recorded to allow a comparison between single- and dual-detector (differential) modes of detection and to demonstrate the improvement achieved with differential detection. Copyright 1999 John Wiley & Sons, Ltd.     

Pseudo-steady-state solutions for solidification in a wedge

Polubarinova-Kochina's analytical differential equation methodis used to determine the pseudo-steady-state solution to problemsinvolving the freezing (solidification) of wedges of liquidwhich are initially at their fusion temperature. In particular,we consider four distinct problems for wedges which are: freezingwith the same constant boundary temperature, freezing with thesame constant boundary heat fluxes, freezing with distinct constantboundary temperatures and freezing with distinct constant fluxesat the boundaries. For the last two problems, a Heun's differentialequation with an unknown singularity is derived, which in bothcases admits a particularly elegant simple solution for thespecial case when the wedge angle is . The moving boundariesobtained are shown pictorially.     

The Hardness of Polynomial Equation Solving

Elimination theory was at the origin of algebraic geometry in the nineteenth century and now deals with the algorithmic solving of multivariate polynomial equation systems over the complex numbers or, more generally, over an arbitrary algebraically closed field. In this paper we investigate the intrinsic sequential time complexity of universal elimination procedures for arbitrary continuous data structures encoding input and output objects of elimination theory (i.e., polynomial equation systems) and admitting the representation of certain limit objects. Our main result is the following: let there be given such a data structure and together with this data structure a universal elimination algorithm, say P, solving arbitrary parametric polynomial equation systems. Suppose that the algorithm P avoids unnecessary branchings and that P admits the efficient computation of certain natural limit objects (as, e.g., the Zariski closure of a given constructible algebraic set or the parametric greatest common divisor of two given algebraic families of univariate polynomials). Then P$ cannot be a polynomial time algorithm. The paper contains different variants of this result and discusses their practical implications.     

Commutative algebras of minimal rank

If $\text{A}$ is a finite-dimensional associative k-algebra with unit, then its rank R($\text{A}$), i.e. its bilinear complexity, is never less than $\text{2dim}\text{A}\text{?\#}\text{M}\text{(}\text{A}\text{)}$. $\text{A}$ is said to be of minimal rank if $\text{R(}\text{A}\text{)=2dim}\text{A}\text{?\#}\text{M}\text{(}\text{A}\text{)}$. In this paper we determine for infinite perfect fields k all commutative k-algebras of minimal rank. Roughly speaking, these algebras are built up from simply generated structures which annihilate each other. Furthermore, we indicate how this result can be used to obtain new lower bounds for the rank of specific commutative algebras.     

Unexpected conversion of a hexacyanometallate to a homoleptic nitrile complex with triphenylborane substituents

The homoleptic, triphenylborane adduct of the hexacyanochromate anion was structurally characterized and found to be a product in which all six cyanide ligands have undergone isomerization to nitrile groups.     

Vibrational circular dichroism in the mid-infrared

Vibrational circular dichroism (VCD) has been measured for the First tune in the CH₂ bending region down to 1250 cm^?1. This advance in technique was facilitated by the addition of a carbon-rod light source, a cooled HgCdTe detector, and signal averaging to our instrument.