Pervasive nonlinear vibrations due to rod-obstacle contact

Nonlinear Dynamics - Simple mechanical contact between a deformable body and a rigid obstacle can lead to rich nonlinear behavior even when the equations governing the body’s motion are...     

Multi-stage stochastic fluid models for congestion control

We consider multi-stage stochastic fluid models (SFMs), driven by applications in telecommunications and manufacturing in which control of the behavior of the system during congestion may be required. In a two-stage SFM, the process starts from Stage 1 in level 0, and moves to Stage 2 when reaching threshold _b2$b_2$ from below. Stage 1 starts again when reaching threshold _b1<_b2$b_1<b_2$ from above. While in a particular stage, the process evolves according to a traditional SFM with a unique set of phases, generator and fluid rates. We first consider a two-stage SFM with general, real fluid change rates. Next, we analyze a two-stage SFM with an upper boundary B>_b2$B>b_2$. Finally, we discuss a generalization to multi-stage SFMs. We use matrix-analytic methods and derive efficient methodology for the analysis of this class of models.     

Structural characterization of Pu[N(SiMe(3))(2)](3), a synthetically useful nonaqueous plutonium(III) precursor

A rare, and synthetically versatile, nonaqueous plutonium complex, Pu[N(SiMe3)2]3 (1), has been structurally characterized by single-crystal X-ray diffraction for the first time and reveals significantly shorter agostic interactions compared to the cerium(III) analogue, indicating possible covalency differences.     

Identification of isomeric N-glycan structures by mass spectrometry with 157 nm laser-induced photofragmentation

Characterization of structural isomers has become increasingly important and extremely challenging in glycobiology. This communication demonstrates the capability of ion-trap mass spectrometry in conjunction with 157 nm photofragmentation to identify different structural isomers of permethylated N-glycans derived from ovalbumin without chromatographic separation. The results are compared with collision-induced dissociation (CID) experiments. Photodissociation generates extensive cross-ring fragment ions as well as diagnostic glycosidic product ions that are not usually observed in CID MS/MS experiments. The detection of these product ions aids in characterizing indigenous glycan isomers. The ion trap facilitates MS(n) experiments on the diagnostic glycosidic fragments and cross-ring product ions generated through photofragmentation, thus allowing unambiguous assignment of all of the isomeric structures associated with the model glycoprotein used in this study. Photofragmentation is demonstrated to be a powerful technique for the structural characterization of glycans.     

Synthesis and structure of (Ph4P)2MCl6 (M = Ti, Zr, Hf, Th, U, Np, Pu)

High-purity syntheses are reported for a series of first, second, and third row transition metal and actinide hexahalide compounds with equivalent, noncoordinating countercations: (Ph(4)P)(2)TiF(6) (1) and (Ph(4)P)(2)MCl(6) (M = Ti, Zr, Hf, Th, U, Np, Pu; 2-8). While a reaction between MCl(4) (M = Zr, Hf, U) and 2 equiv of Ph(4)PCl provided 3, 4, and 6, syntheses for 1, 2, 5, 7, and 8 required multistep procedures. For example, a cation exchange reaction with Ph(4)PCl and (NH(4))(2)TiF(6) produced 1, which was used in a subsequent anion exchange reaction with Me(3)SiCl to synthesize 2. For 5, 7, and 8, synthetic routes starting with aqueous actinide precursors were developed that circumvented any need for anhydrous Th, Np, or Pu starting materials. The solid-state geometries, bond distances and angles for isolated ThCl(6)(2-), NpCl(6)(2-), and PuCl(6)(2-) anions with noncoordinating counter cations were determined for the first time in the X-ray crystal structures of 5, 7, and 8. Solution phase and solid-state diffuse reflectance spectra were also used to characterize 7 and 8. Transition metal MCl(6)(2-) anions showed the anticipated increase in M-Cl bond distances when changing from M = Ti to Zr, and then a decrease from Zr to Hf. The M-Cl bond distances also decreased from M = Th to U, Np, and Pu. Ionic radii can be used to predict average M-Cl bond distances with reasonable accuracy, which supports a principally ionic model of bonding for each of the (Ph(4)P)(2)MCl(6) complexes.     

Generalized continuity for Multifunctions

The aim of this paper is to introduce two kinds of generalized continuity for multifunctions. Basic properties and characterizations of such multifunctions are established. These two generalized continuities include many of the variations of multifunction continuity already in the literature as special cases.