Ejection of solvated ions from electrosprayed methanol/water nanodroplets studied by molecular dynamics simulations

The ejection of solvated small ions from nanometer-sized droplets plays a central role during electrospray ionization (ESI). Molecular dynamics (MD) simulations can provide insights into the nanodroplet behavior. Earlier MD studies have largely focused on aqueous systems, whereas most practical ESI applications involve the use of organic cosolvents. We conduct simulations on mixed water/methanol droplets that carry excess NH(4)(+) ions. Methanol is found to compromise the H-bonding network, resulting in greatly increased rates of ion ejection and solvent evaporation. Considerable differences in the water and methanol escape rates cause time-dependent changes in droplet composition. Segregation occurs at low methanol concentration, such that layered droplets with a methanol-enriched periphery are formed. This phenomenon will enhance the partitioning of analyte molecules, with possible implications for their ESI efficiencies. Solvated ions are ejected from the tip of surface protrusions. Solvent bridging prior to ion secession is more extensive for methanol/water droplets than for purely aqueous systems. The ejection of solvated NH(4)(+) is visualized as diffusion-mediated escape from a metastable basin. The process involves thermally activated crossing of a ~30 kJ mol(-1) free energy barrier, in close agreement with the predictions of the classical ion evaporation model.     

Synthetic studies towards oxazinins. An expedient first total synthesis and proof of the absolute stereochemistry of oxazinin-3

A synthetic strategy, based on intramolecular addition of an appropriate hydroxyl substituent to a 3-methyleneindolenine, towards the naturally occurring marine toxins oxazinin-1, -2 and -3 is presented. The expedient first total synthesis of oxazinin-3, thus accomplished, demonstrated the efficiency of the approach and established the absolute stereochemistry of oxazinin-3 as 2S,5S.     

Twistor spinors on Lorentzian symmetric spaces

An indecomposable Riemannian symmetric space which admits non-trivial twistor spinors has constant sectional curvature. Furthermore, each homogeneous Riemannian manifold with parallel spinors is flat. In the present paper we solve the twistor equation on all indecomposable Lorentzian symmetric spaces explicitly. In particular, we show that there are — in contrast to the Riemannian case — indecomposable Lorentzian symmetric spaces with twistor spinors, which have non-constant sectional curvature and non-flat and non-Ricci flat homogeneous Lorentzian manifolds with parallel spinors.     

Preregularization and the path integral approach to the chiral anomaly

We explore the connection between perturbative and non-perturbative (path-integral) approaches to the axial anomaly. In particular, we show how the Jacobian associated with the fermionic measure corresponding to local axial transformations may be calculated directly from shift-of-integration-variable surface terms in four Euclidean dimensions. No regularization (explicit parametrization of UV infinities) is required in this approach, but invariance of the Jacobian under vector gauge transformations (i.e. preregularization) is required to remove a variable-of-integration ambiguity within the expression for the Jacobian of the fermionic measure.     

Cross-recurrence plot quantification analysis of input and output signals for the detection of chatter in turning

Metal cutting is a complex nonlinear dynamical process. Analysis of signals from turning operation shows that the machining exhibits a low-dimensional chaos. The self-excited vibration caused by the regenerative effect, usually called chatter, can be created during machining by increasing one cutting parameter, while keeping all other cutting parameters constant. A cross-recurrence plot (CRP) enables the study of synchronisation or time differences in two time series. CRP-based methodology is used to find the point of transition from normal cutting to chatter cutting. In this method, two signals, one input signal (power to the lathe motor) and one output signal (cutting tool vibration), are recorded simultaneously at a constant sampling rate during cutting. A time series is generated from the recorded values, and cross-recurrence plot is prepared. This CRP can be quantified using Cross-Recurrence Quantification Analysis (CRQA). Abrupt variation in the CRQA parameters indicates the onset of chatter vibration. The results are verified using permutation entropy (PE) to detect the onset of chatter from the time series. The present study ascertains that this CRP-based methodology is capable of recognising the transition from regular cutting to the chatter cutting irrespective of the machining parameters or work piece material.     

Benefits of Objective Collapse Models for Cosmology and Quantum Gravity

We display a number of advantages of objective collapse theories for the resolution of long-standing problems in cosmology and quantum gravity. In particular, we examine applications of objective reduction models to three important issues: the origin of the seeds of cosmic structure, the problem of time in quantum gravity and the information loss paradox; we show how reduction models contain the necessary tools to provide solutions for these issues. We wrap up with an adventurous proposal, which relates the spontaneous collapse events of objective collapse models to microscopic virtual black holes.     

Synthesis and Characterisation of Two Examples of Unsymmetrically Disubstituted Cyclotetrathiazenes, 1,5-(X)(Y)S4N4[X = Ph3PN- and Y = i) (p-CH3C6H4) Ph2PN- and ii) (P-CH3C6H4)2PhPN-]

Abstract

1,5- [(p-tolyl)diphenylphosphinimino] (triphenylphosphinimino)tetrasulphurtetranitride, (I) and 1,5-[di(p-tolyl)phenylphosphinimino] (triphenylphosphinimino)tetrasulphurtetranitride, (II) are the first examples of heterodisubstituted tetrasulphurtetranitride derivatives to be made. Their synthesis and structural characterization are described.     

Cross-Linking of Poly(α-amino Acids)

Poly(L-leucine) and poly(L-phenylalanine) cross-link with either 2,4-toluene diisocyanate or 1,6-hexane diisocyanate but no such cross-linking resulted for poly(γ-benzyl-L-glutamate). The latter polymer cross-links, however, upon transesterification with diols.