Apparatur zur säulenelektrophorese in nichtwässrigen lösungsmitteln

An apparatus for electrophoresis in non-aqueous solvents is described, which makes it possible to work in field strengths up to 150 V/cm and at temperatures down to ?50°. A flow-through cell with two double “Suprasil” windows facilitates the photometric evaluation of the separations, and keeps the sample cool until it reaches the detection system. Potassium Polysulphides have been separated as an example of salts sensitive to hydrolysis, thiocyanato(phenylenediamine)chromium(III) complexes as an example of salts only slightly soluble in water, and aromatic sulphonates as an example of salts complexed by crown compounds.     

Sensitivity of in-Plane Strain Measurement to Calibration Parameter for out-of-Plane Specimen Rotations

In practice, out-of-plane motions usually are not avoidable during experiments. Since 2D–DIC measurements are vulnerable to parasitic deformations due to out-of-plane specimen motions, three-dimensional digital image correlation (StereoDIC or 3D–DIC) oftentimes is employed. The StereoDIC method is known to be capable of accurate deformation measurements for specimens subjected to general three-dimensional motions, including out-of-plane rotations and displacements. As a result, there has been limited study of the deformation measurements obtained when using StereoDIC to measure the displacement and strain fields for a specimen subjected only to out-of-plane rotation. To assess the accuracy of strain measurements obtained using stereovision systems and StereoDIC when a specimen undergoes appreciable out of plane rotation, rigid body out-of-plane rotation experiments are performed in the range ?40⁰?≤?θ?≤?40⁰ using a two-camera stereovision system. Results indicate that (a) for what would normally be considered “small angle” calibration processes, the measured normal strain in the foreshortened specimen direction due to specimen rotation increases in a non-linear manner with rotation angle, with measurement errors exceeding ±1400με and (b) for what would normally be considered “large angle” calibration processes, the magnitude of the errors in the strain are reduced to ±300με. To theoretically assess the effect of calibration parameters on the measurements, two separate analyses are performed. First, theoretical strains due to out-of-plane rigid body rotation are determined using a pinhole camera model to project a series of three-dimensional object points into the image plane using large angle calibration parameters and then re-project the corresponding sensor plane coordinates back into the plane using small angle calibration parameters. Secondly, the entire imaging process is also simulated in order to remove experimental error sources and to further validate the theory. Results from both approaches confirmed the same strain error trends as the experimental strain measurements, providing confidence that the source of the errors is the calibration process. Finally, variance based sensitivity analyses show that inaccuracy in the calibrated stereo angle parameter is the most significant factor affecting the accuracy of the measured strain.     

High pressure μSR studies: rare earths and related materials

After a short introduction to μSR with respect to the study of magnetic properties, followed by a brief outline of the principle of the high pressure-low temperature μSR spectrometer installed at the Paul Scherrer Institute, we discuss some measurements on rare earth materials employing this instrument. They are concerned with: (1) The pressure dependence of the spin turning process in ferromagnetic Gd. (2) The volume dependence of the internal magnetic field in the heavy rare earth metals Gd, Dy, and Ho in their ordered magnetic states. (3) The response of the (first order) magnetic transition in the frustrated antiferromagnets of type RMn₂ (R = Y,Gd) to pressure. (4) The variation of magnetic parameters with pressure in La₂CuO₄ (powder sample), the antiferromagnetic parent compound of the high T_C superconductors of type La_2−x(Sr, Ba)_xCuO₄. In conclusion a short outlook on further developments is given. This revised version was published online in July 2006 with corrections to the Cover Date.     

On-line adaptive digital correction of dual-quantisation delta-sigma modulators

The authors describe the digital adaptive correction of nonidealities in dual-quantisation delta-sigma modulators. The sources and effects of nonidealities in a delta-sigma loop are discussed, and a simple on-line correction scheme is presented. The theoretical signal-to-noise ratio (SNR) improvement is calculated and simulation results are given which illustrate the effectiveness of the technique.<>     

A photocontrolled beta-hairpin peptide

Beta-hairpins constitute the smallest beta-type structures in peptides and proteins. The development of highly stable, yet monomeric beta-hairpins based on the tryptophan zipper motif was therefore a remarkable success [A. G. Cochran, N. J. Skelton, M. A. Starovasnik, Proc. Natl. Acad. Sci USA 2001, 98, 5578-5583]. We have been able to design, synthesize and characterize a hairpin based on this motif which incorporates an azobenzene-based photoswitch, that allows for time-resolved folding studies of beta-structures with unprecedented time resolution. At room temperature the trans-azo isomer exhibits a mostly disordered structure; however, light-induced isomerization to the cis-azo form leads to a predominantly extended and parallel conformation of the two peptide parts, which are linked by the novel photoswitch, [3-(3-aminomethyl)phenylazo]phenylacetic acid (AMPP). While in the original sequence the dipeptide Asn-Gly forms a type I' beta-turn which connects the two strands of the hairpin, this role is adopted by the AMPP chromophore in our photoresponsive beta-hairpin that can apparently act as a beta I'-turn mimetic. The beta-hairpin structure was determined and confirmed by NMR spectroscopy, but the folding process can be monitored by pronounced changes in the CD, IR and fluorescence spectra. Finally, incorporation of the structurally and functionally important beta-hairpin motif into proteins by chemical ligation might allow for the photocontrol of protein structures and/or functions.