Alternating layer and island growth of Pb on Si by spontaneous quantum phase separation

Real-time in situ x-ray studies of continuous Pb deposition on Si(111)-(7x7) at 180 K reveal an unusual growth behavior. A wetting layer forms first to cover the entire surface. Then islands of a fairly uniform height of about five monolayers form on top of the wetting layer and grow to fill the surface. The growth then switches to a layer-by-layer mode upon further deposition. This behavior of alternating layer and island growth can be attributed to spontaneous quantum phase separation based on a first-principles calculation of the system energy.     

High-resolution diffusion imaging using phase-corrected segmented echo-planar imaging

Diffusion magnetic resonance imaging (MRI) was performed with a high-resolution segmented echo-planar imaging technique, which provided images with substantially less susceptibility artifacts than images obtained with single-shot echo-planar imaging (EPI). Diffusion imaging performed with any multishot pulse sequence is inherently sensitive to motion artifacts and in order to reduce motion artifacts, the presented method utilizes navigator echo phase corrections, performed after a one-dimensional Fourier transform along the frequency-encoding direction. Navigator echo phases were fitted to a straight line prior to phase correction to avoid errors from internal motion. In vivo imaging was performed using electro cardiographic (ECG) triggering. Apparent diffusion coefficient (ADC) maps were calculated on a pixel-by-pixel basis using up to seven diffusion sensitivities, ranging from b = 0 to 1129 x 10(6) s/m(2).     

Optimal closing of a pair trade with a model containing jumps

A pair trade is a portfolio consisting of a long position in one asset and a short position in another, and it is a widely used investment strategy in the financial industry. Recently, Ekström, Lindberg, and Tysk studied the problem of optimally closing a pair trading strategy when the difference of the two assets is modelled by an Ornstein-Uhlenbeck process. In the present work the model is generalized to also include jumps. More precisely, we assume that the difference between the assets is an Ornstein-Uhlenbeck type process, driven by a Lévy process of finite activity. We prove a necessary condition for optimality (a so-called verification theorem), which takes the form of a free boundary problem for an integro-differential equation. We analyze a finite element method for this problem and prove rigorous error estimates, which are used to draw conclusions from numerical simulations. In particular, we present strong evidence for the existence and uniqueness of an optimal solution.     

MICROEMULSIONS: A CONTEMPORARY OVERVIEW

The literature on microemulsions from 1975-1979 has been reviewed.     

Interpolation of coefficients and transformation of the dependent variable in finite element methods for the non-linear heat equation

Error estimates are shown for some spatially discrete Galerkin finite element methods for a non-linear heat equation. The approximation schemes studied are based on the introduction of the enthalpy as a new dependent variable, and also on the application of the Kirchhoff transformation and on interpolation of the non-linear coefficients into standard Lagrangian finite element spaces.     

Potentiometrie

Ohne Zusammenfassung     

Measurement of penbutolol and 4-hydroxypenbutolol in plasma or serum by HPLC

A simple HPLC method for penbutolol and 4-hydroxypenbutolol assay has been developed. Plasma or serum (200 microliters) is vortex-mixed (30 s) with Tris solution (2 M, pH 10.6) containing an internal standard (50 microliters) and methyl t-butyl ether (200 microliters). After centrifugation, the extract (100 microliters) is analysed using an unmodified silica column (250 x 5 mm ID) and iso-octane-methanol-methyl t-butyl ether (55:25:20) containing ammonium perchlorate (10 mM, pH 5.7) as eluent and with fluorescence detection. No interference has been encountered and the limit of accurate measurement for both compounds is 5 micrograms/l.     

Diethyl 4‐(2,5‐di­methoxy­phenyl)‐2,6‐di­methyl‐1,4‐di­hydro­pyridine‐3,5‐di­carboxyl­ate,conformational change with solvent of crystallization

The title compound, C₂₁H₂₇NO₆, has been crystallized from ethanol containing nitro­benzene and shows the phenyl ring, B, in an ap conformation. This structure may be compared with that of the mol­ecule crystallized from ethanol alone, in which the B ring is seen in an sp conformation. The isolation of this rotamer has implications for the understanding of the docking of calcium beta‐blocking di­hydro­pyridine mol­ecules with their receptor site.