The Ternary System Nickel/Silicon/Titanium Revisited

The constitution of the ternary system Ni/Si/Ti is investigated over the entire composition range using X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDS), differential thermal analysis (DTA), and metallography. The solid state phase equilibria are determined for 900 °C. Eight ternary phases are found to be stable. The crystal structures for the phases τ₁NiSiTi, τ₂Ni₄Si₇Ti₄, τ₃Ni₄₀Si₃₁Ti₁₃, τ₄Ni₁₇Si₇Ti₆, and τ₅Ni₃SiTi₂ are corroborated. For the remaining phases the compositions are determined as Ni₆Si₄₁Ti₅₃ (τ₆), Ni₁₆Si₄₂Ti₄₂(τ₇), and Ni₁₂Si₄₅Ti₄₃ (τ₈). The reaction scheme linking the solid state equilibria with the liquidus surface is amended to account for these newly observed phases. The discrepancies between previous experimental conclusions and modeling results are addressed. The liquidus surface is dominated by the primary crystallisation field of τ₁NiSiTi, the only congruently melting phase.     

Effect of N-terminal glutamic acid and glutamine on fragmentation of peptide ions

A prominent dissociation path for electrospray generated tryptic peptide ions is the dissociation of the peptide bond linking the second and third residues from the ammo-terminus. The formation of the resulting b₂ and y _n−2 fragments has been rationalized by specific facile mechanisms. An examination of spectral libraries shows that this path predominates in diprotonated peptides composed of 12 or fewer residues, with the notable exception of peptides containing glutamine or glutamic acid at the N-terminus. To elucidate the mechanism by which these amino acids affect peptide fragmentation, we synthesized peptides of varying size and composition and examined their MS/MS spectra as a function of collision voltage in a triple quadrupole mass spectrometer. Loss of water from N-terminal glutamic acid and glutamine is observed at a lower voltage than any other fragmentation, leading to cyclization of the terminal residue. This cyclization results in the conversion of the terminal amine group to an imide, which has a lower proton affinity. As a result, the second proton is not localized at the N-terminus but is readily transferred to other sites, leading to fragmentation near the center of the peptide. Further confirmation was obtained by examining peptides with N-terminal pyroglutamic acid and N-acetyl peptides. Peptides with N-terminal proline maintain the trend of forming b₂ and y _n−2 because their ring contains an imine rather than imide and has sufficient proton affinity to retain the proton at the N-terminus.     

Hydrophilization of Magnetic Nanoparticles with Modified Alternating Copolymers. Part 1: The Influence of the Grafting

Iron oxide nanoparticles (NPs) with a diameter 21.6 nm were coated with poly(maleic acid-alt-1-octadecene) (PMAcOD) modified with grafted 5,000 Da poly(ethyelene glycol) (PEG) or short ethylene glycol (EG) tails. The coating procedure utilizes hydrophobic interactions of octadecene and oleic acid tails, while the hydrolysis of maleic anhydride moieties as well as the presence of hydrophilic PEG (EG) tails allows the NP hydrophilicity. The success of the NP coating was found to be independent of the degree of grafting which was varied between 20 and 80% of the -MacOD-units, but depended on the length of the grafted tail. The NP coating and hydrophilization did not occur when the modified copolymer contained 750 Da PEG tails independently of the grafting degree. To explain this phenomenon the micellization of the modified PMAcOD copolymers in water was analyzed by small angle x-ray scattering (SAXS). The PMAcOD molecules with the grafted 750 Da PEG tails form compact non-interacting disk-like micelles, whose stability apparently allows for no interactions with the NP hydrophobic shells. The PMAcOD containing the 5,000 Da PEG and EG tails form much larger aggregates capable of an efficient coating of the NPs. The coated NPs were characterized using transmission electron microscopy, dynamic light scattering, ζ-potential measurements, and thermal gravimetry analysis. The latter method demonstrated that the presence of long PEG tails in modified PMAcOD allows the attachment of fewer macromolecules (by a factor of ~20) compared to the case of non-modified or EG modified PMAcOD, emphasizing the importance of PEG tails in NP hydrophilization. The NPs coated with PMAcOD modified with 60% (towards all -MAcOD- units) of the 5,000 PEG tails bear a significant negative charge and display good stability in buffers. Such NPs can be useful as magnetic cores for virus-like particle formation.     

Coulomb forces on DNA polymers in charged fluidic nanoslits

We investigate the repulsive electrostatic interactions between a DNA polyelectrolyte and the charged walls of a fluidic nanoslit. The scaling of the DNA coil size with the physical slit height revealed electrostatic depletion regions that reduced the effective slit height. These regions exceeded the Debye screening length of the buffer, λ(D)(buffer), and saturated at ≈ 50 nm when λ(D)(buffer) reached 10 nm. We explain these results by modeling a semiflexible charged rod near a charged wall and the electrostatic screening by the polyelectrolyte. These results demonstrate the surprisingly long range over which a nanofluidic device can exert field-effect control over confined molecules.     

List Edge‐Coloring and Total Coloring in Graphs of Low Treewidth

We prove that the list chromatic index of a graph of maximum degree Δ and treewidth is Δ; and that the total chromatic number of a graph of maximum degree Δ and treewidth is . This improves results by Meeks and Scott.     

A Heuristic for Moment-Matching Scenario Generation

In stochastic programming models we always face the problem of how to represent the random variables. This is particularly difficult with multidimensional distributions. We present an algorithm that produces a discrete joint distribution consistent with specified values of the first four marginal moments and correlations. The joint distribution is constructed by decomposing the multivariate problem into univariate ones, and using an iterative procedure that combines simulation, Cholesky decomposition and various transformations to achieve the correct correlations without changing the marginal moments.With the algorithm, we can generate 1000 one-period scenarios for 12 random variables in 16 seconds, and for 20 random variables in 48 seconds, on a Pentium III machine.     

Depth profile investigations of metallic layer contacts to GaAs(100) and InP(100) by means of Auger Electron Spectroscopy and sputter technique

Summary The present technological development in the field of opto-electronics requires a sufficiently high stability of the applied metal-semiconductor contacts because of the thermal and electrical cross-section loading. Au/Pt/Ti layer contacts to GaAs(100) and InP(100) substrates annealed under various conditions were investigated by means of Auger Electron Spectroscopy (AES) in conjunction with ion sputtering. The diffusion and reaction behavior are discussed based on intensity-depth profiles and chemical shifts. As the main result we found that the GaAs contact is more stable. It reacts strongly at a temperature of about 450°C. On the other hand Au/Pt/Ti/InP contact reacts already above 300°C. The principal reason for the difference in the behavior of InP and GaAs contacts is the In segregation.