Optimal doping control of magnetic semiconductors via subsurfactant epitaxy

"Subsurfactant epitaxy" is established as a conceptually new approach for introducing manganese as a magnetic dopant into germanium. A kinetic pathway is devised in which the subsurface interstitial sites on Ge(100) are first selectively populated with Mn, while lateral diffusion and clustering on or underneath the surface are effectively suppressed. Subsequent Ge deposition as a capping layer produces a novel surfactantlike phenomenon as the interstitial Mn atoms float towards newly defined subsurface sites at the growth front. Furthermore, the Mn atoms that failed to float upwards are uniformly distributed within the Ge capping layer. The resulting doping levels of order 0.25 at. % would normally be considered too low for ferromagnetic ordering, but the Curie temperature exceeds room temperature by a comfortable margin. Subsurfactant epitaxy thus enables superior dopant control in magnetic semiconductors.     

A new derivatization strategy for the analysis of phosphopeptides by precursor ion scanning in positive ion mode

Although numerous strategies have been devised to analyze protein phosphorylation, an abundant intracellular protein modification, there is still a need for different methods for the analysis of this modification. A method to both detect and localize the phosphorylation within a protein/peptide is especially required. In this paper, a new strategy is described, which makes use of beta-elimination/Michael addition reactions to introduce a functional group at the original site of phosphorylation, which gives rise to a dimethylamine-containing sulfenic acid derivative with a unique m/z value. This enables the detection of the phosphorylated species within peptide mixtures by sensitive and specific precursor ion scanning in positive ion mode. Working under acidic conditions in positive ion mode has the added advantage that subsequent normal peptide sequencing for the exact localization can be performed. No other peptide derived fragment ion is observed at the m/z value of the sulfenic acid derivative formed, thus specific precursor ion experiments can also be carried out on instruments with low fragment ion resolution and lends itself to LC-MS/MS approaches when skimmer fragmentation routines or triple quadrupole mass spectrometers are used.     

High-Resolution Phase Doppler Particle Sizing based on Hilbert transform signal processing

A new phase Doppler anemometry (PDA) signal processing method based on a Hilbert transform algorithm is introduced and analysed. By generating a 90° phase-shifted burst signal in the time domain, the envelope of the Doppler burst can be determined. In addition, this envelope is approximated by a Gaussian exponential function. The difference of the maxima of these Gaussian approximations for two related PDA bursts gives an estimate of the time difference between these time shifted signals. With the introduction of this estimation method, the restriction to the [0,360°] interval resulting from conventional signal analysis may be avoided in many cases. To investigate the dependence on SNR, burst position, burst frequency and sampling rate, results of computer simulations are presented. The feasibility of the method is demonstrated briefly by experimental results. Phase differences of more than 2000° arising from the measurement of monodisperse droplets by a conventional PDA setup could be determined.     

Effective shell charge of electrons on a sphere

By ignoring the radial motions of the electrons in the valence shell of an atom one formally obtains the problem of electrons constrained to move on a sphere. This sphere will be attracted by the core as if it had an effective charge equal to the number of electrons on it minus a certain quantity resulting from the mutual repulsion of the electrons. This “effective shell charge” is a very simple, but still precise and quantitative concept which provides a good understanding of many empirical facts about atoms and ions, most notably Hund's rules. Implications for negative ions are discussed and chemical bonding is touched briefly. A qualitative difference in physical behavior for small and large sphere radii is pointed out.     

Difference gel electrophoresis identifies differentially expressed proteins in endoscopically collected pancreatic fluid

Alterations in the pancreatic fluid proteome of individuals with chronic pancreatitis (CP) may offer insights into the development and progression of the disease. The endoscopic pancreatic function test (ePFT) can safely collect large volumes of pancreatic fluid that are potentially amenable to proteomic analyses using difference gel electrophoresis (DIGE) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Pancreatic fluid was collected endoscopically using the ePFT method following secretin stimulation from three individuals with severe CP and three chronic abdominal pain (CAP) controls. The fluid was processed to minimize protein degradation and the protein profiles of each cohort, as determined by DIGE and LC-MS/MS, were compared. This DIGE-LC-MS/MS analysis reveals proteins that are differentially expressed in CP compared with CAP controls. Proteins with higher abundance in pancreatic fluid from CP individuals include: actin, desmoplankin, α-1-antitrypsin, SNC73, and serotransferrin. Those of relatively lower abundance include carboxypeptidase B, lipase, α-1-antichymotrypsin, α-2-macroglobulin, actin-related protein (Arp2/3) subunit 4, glyceraldehyde-3-phosphate dehydrogenase, and protein disulfide isomerase. Endoscopic collection (ePFT) in tandem with DIGE-LC-MS/MS is a suitable approach for pancreatic fluid proteome analysis; however, further optimization of our protocol, as outlined herein, may improve proteome coverage in future analyses.     

Epitaxial stabilization of ferromagnetism in the nanophase of FeGe

Epitaxial nanocrystals of FeGe have been stabilized on Ge(111). The nanocrystals assume a quasi-one-dimensional shape as they grow exclusively along the <110> direction of the Ge(111) substrate, culminating in a compressed monoclinic modification of FeGe. Whereas monoclinic FeGe is antiferromagnetic in the bulk, the nanowires are surprisingly strong ferromagnets below approximately 200 K with an average magnetic moment of 0.8 microB per Fe atom. Density functional calculations indicate an unusual stabilization mechanism for the observed ferromagnetism: lattice compression destabilizes the antiferromagnetic Peierls-like ground state observed in the bulk while increased p-d hybridization suppresses the magnetic moments and stabilizes ferromagnetism.