Thermodynamics of aqueous solutions of methyldiethanolamine and diisopropanolamine

The vapour–liquid equilibrium (VLE) of the systems of water + methyldiethanolamine (MDEA) and water + diisopropanolamine (DIPA) was measured at several temperatures with a static total pressure apparatus. The solid–liquid equilibrium (SLE) of the same systems was measured at low amine concentrations by means of two experimental methods: a visual method and a Differential Scanning Calorimeter (DSC). The activity coefficients of water + MDEA were modelled with the NRTL equations. The model parameters were regressed from VLE, SLE and excess enthalpy data from this work and from the literature. The model developed in this work was compared with models found in the literature. The NRTL equations were also used to model the activity coefficients of the system of water + DIPA. The model parameters were fitted from the VLE and SLE data measured in this work.     

Environmental and food analysis by desorption atmospheric pressure photoionization‐mass spectrometry

Desorption atmospheric pressure photoionization‐mass spectrometry (DAPPI‐MS) is a versatile surface analysis technique for a wide range of analytes, especially for neutral and non‐polar analytes. Here, a set of analytes typically found in environmental or food samples was analyzed by DAPPI‐MS. The set included five polyaromatic hydrocarbons (PAHs), one N‐PAH, one brominated flame retardant, and nine pesticides, which were studied with three different spray solvents: acetone and toluene in positive ion mode, and anisole in negative ion mode. The analytes showed [M + H]⁺, M^+?, and [M–H]^? ions as well as fragmentation and substitution products. Detection limits for the studied compounds ranged from 30 pg to 1 ng (from 0.14 to 5.6 pmol). To demonstrate the feasibility of the use of DAPPI‐MS two authentic samples – a circuit board and orange peel – and a spiked soil sample were analyzed. Tetrabromobisphenol A, imazalil, and PAHs were observed from the three above‐mentioned samples, respectively. The method is best suited for rapid screening analysis of environmental or food samples. Copyright © 2010 John Wiley & Sons, Ltd.     

Interpretation of orientational contrast in STM images of GaAs(1 1 0) cleavage surface

The electronic structure of GaAs(1 1 0) surface is analyzed using Density Functional Theory (DFT-GGA) in atomic orbital basis (LCAO). The surface orbitals and the corresponding local density of electronic states (LDOS) are calculated for purposes of interpreting STM images. We show how local atomic orbitals of surface atoms are related to tunneling channels for electrons in STM imaging. A destructive interference between orbitals of two neighbouring atoms increases the contrast between the two atoms, and this is reflected in directionality of STM patterns of GaAs(1 1 0) surfaces. We also discuss how the basic formalism of Tersoff-Hamann approach to STM simulation can be reformulated to reveal the role of phase difference between tunneling channels.     

Cross‐sectional high‐resolution microscopy of thin pretreatment layers on hot dip galvanized steel

Hexavalent chromium containing pretreatments and primers for coil coating are soon to be entirely prohibited, which sets new demands for Cr‐free alternatives. Most of the presently used Cr‐free pretreatment layers operate predominantly via barrier formation and adhesion promotion mechanisms and lack the self‐healing effect typical for Cr⁶⁺‐pretreatments. This sets new demands also for the formation and monitoring of these layers. The barrier thickness and chemical composition of Cr‐free pretreatment layers on hot dip galvanized steel were studied using cross sections from broad ion beam (BIB) sample preparation and ultramicrotome cutting. BIB milling provided finely polished cross sections of pretreated samples. Film thicknesses of 20–50 nm were accurately determined for Cr‐free pretreatments containing 4–10 mg Ti/m² using BIB milling and scanning electron microscopy imaging. Scanning transmission electron microscopy, integrated with aberration correctors and X‐ray energy dispersive spectrometry, of an ultramicrotome cut pretreated and painted samples provided detailed chemical information. Metal complexes were detected close to the pretreatment/zinc interface, while the polymeric part of the pretreatment layer prevailed closer to paint. Copyright © 2014 John Wiley & Sons, Ltd.     

Ultrafast Two‐Dimensional NMR Relaxometry for Investigating Molecular Processes in Real Time

Nuclear spin–lattice (T₁) and spin–spin (T₂) relaxation times provide versatile information about the dynamics and structure of substances, such as proteins, polymers, porous media, and so forth. Multidimensional experiments increase the information content and resolution of NMR relaxometry, but they also multiply the measurement time. To overcome this issue, we present an efficient strategy for a single‐scan measurement of a 2D T₁–T₂ correlation map. The method shortens the experimental time by one to three orders of magnitude as compared to the conventional method, offering an unprecedented opportunity to study molecular processes in real‐time. We demonstrate that, despite the tremendous speed‐up, the T₁–T₂ correlation maps determined by the single‐scan method are in good agreement with the maps measured by the conventional method. The concept of the single‐scan T₁–T₂ correlation experiment is applicable to a broad range of other multidimensional relaxation and diffusion experiments.     

Passive Advection and the Degenerate Elliptic Operators <Emphasis Type="Italic">M</Emphasis><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

 We prove estimates for the stationary state n-point functions at zero molecular diffusivity in the Kraichnan model [13]. This is done by proving upper bounds for the heat kernels and Green's functions of the degenerate elliptic operators M _n that occur in the Hopf equations for the n-point functions. Received: 25 August 2001 / Accepted: 30 September 2002 Published online: 20 January 2003 Communicated by A. Kupiainen     

Effect of Droplet Size and Atomization on Spray Formation: A Priori Study Using Large-Eddy Simulation

The paper is mainly focused to the vast number of researchers who work within direct injection (DI) engine fuel spray simulations. The most common simulation framework today within the community is the Reynolds Averaged Navier Stokes (RANS) approach together with the Lagrangian Particle Tracking (LPT) method. In fact, this study is one of the first studies where high resolution LES/LPT diesel spray modeling is considered. The potential of LES to deepen the present day multidimensional LPT fuel spray simulations is discussed. Spray evolution is studied far from an injector by modeling a spray as a particle laden jet (PLJ). The effect of d on mixing in non-atomizing and atomizing sprays is thoroughly investigated at jet inlet Reynolds number Re?=?10⁴ and Mach number Ma?=?0.3. Based on and justified by rather recent and also quite old ideas, novel and compact views on droplet breakup in turbulent flows are pointed out from the literature. We use LES/LPT to illustrate that even in a low Weber number flow (We?<?13) the droplet breakup modeling may need considerable attention in contrast to what is typically assumed in the present-day breakup models. LES and LPT techniques are first applied to essentially confirm certain expected droplet size effects on spray shape in non-atomizing monodisperse sprays. In the simulations LES e.g. produces an expected turbulent dispersion pattern that depends on droplet diameter (d) without a droplet dispersion model in contrast to RANS. A new compact droplet breakup model is formulated and tested for droplets that break with a natural resonance time rate according to the Poisson process. As a result of the study: 1) the analysis gives a rigorous and enriching proof of currently existing views on droplet size effects on mixing, and 2) the presented a priori analysis points out the importance of modeling the resonance breakup even at a low We.     

All-electron time-dependent density functional theory with finite elements: time-propagation approach

We present an all-electron method for time-dependent density functional theory which employs hierarchical nonuniform finite-element bases and the time-propagation approach. The method is capable of treating linear and nonlinear response of valence and core electrons to an external field. We also introduce (i) a preconditioner for the propagation equation, (ii) a stable way to implement absorbing boundary conditions, and (iii) a new kind of absorbing boundary condition inspired by perfectly matched layers.