Self pulsing in second harmonic generation

We consider nonlinear optical processes in a cavity maintained far from thermal equilibrium by external pumping. In second harmonic generation we predict a hard mode instability at a critical pump strength indicating the existence of undamped spiking similar to that in strongly pumped lasers. In subharmonic generation above the soft mode transition noted by Graham we predict the appearance of sidebands in the subharmonic spectrum.     

Production of squeezed states in a degenerate parametric amplifier

An analysis of the degenerate parametric amplifier including the quantisation of pump and signal modes is presented. It is shown that the fluctuations in one quadrature of the signal mode may be reduced at most by a factor of two. This is in contradistinction to analyses where the pump field is treated classically which overestimate the reduction in fluctuations possible.     

Artifacts in four-sector tandem mass spectrometry

Several types of artifacts were shown to be present in 4-sector tandem collision-induced dissociation (CID) mass spectra. In CID spectra of protonated peptides produced by liquid secondary-ion mass spectrometry (LSIMS), peaks corresponding to successive losses of matrix molecules from the precursor ion were observed. In addition, peaks corresponding to MH+ ions of smaller peptides that were also present in the sample/matrix mixture in greater abundance than the selected precursor ion were observed. Both of these types of artifact peaks were shown to originate from the 'peak-at-every-mass' chemical noise at the same nominal mass as that selected by the first 2 sectors (MS1). These noise ions are transmitted through to the collision cell and produce fragments that are analysed and detected in the next 2 sectors (MS2). A second, unrelated, kind of artifact was found to be due to decompositions in the second field-free region of MS2 in an EBEB geometry machine. These artifacts, which are detectable over only a very limited mass range when using a conventional single-point detector, can be present over a much greater mass range when an array detector is used and when the collision cell is floated above ground potential. A clear understanding of the origins of all peaks in a CID spectrum is important in order to have a firm foundation for interpretation, manual or computer-aided, of the spectra of unknown compounds.     

Nonequilibrium phase transitions in chemical reactions

The far from equilibrium steady states of a simple nonlinear chemical system are analyzed. A standard macroscopic analysis shows that the nonlinearity introduces an instability which causes a transition analogous to a thermodynamic second-order phase transition. Fluctuations are introduced into this model through a stochastic master equation approach. The solution of this master equation in the steady state reveals that the system goes into a more ordered state above the transition point. An analogy is drawn with the nonequilibrium phase transition occurring in the laser at threshold.Supported by a New Zealand U.G.C. Postgraduate Scholarship.     

Stochastic models of firstorder nonequilibrium phase transitions in chemical reactions

The steady states of a simple nonlinear chemical system kept far from equilibrium are analyzed. A standard macroscopic analysis shows that the nonlinearity introduces an instability causing a transition analogous to a thermodynamic first-order phase transition. Near this transition the system exhibits hysteresis between two alternative steady states. Fluctuations are introduced into this model using a stochastic master equation. The solution of this master equation is unique, preventing two alternative exactly stable states. However, a quasi-hysteresis occurs involving transitions between alternative metastable steady states on a time scale that is longer than that of the fluctuations around the mean steady state values by a factor of the forme , where ø is the height of a generalized thermodynamic potential barrier between the two states. In the thermodynamic limit this time scale tends to infinity and we have essentially two alternative stable steady states.     

Seleninate in place of phosphate: irreversible inhibition of protein tyrosine phosphatases

A homotyrosine based seleninic acid irreversibly inhibits protein tyrosine phosphatases by forming a covalent selenosulfide linkage with the active site cysteine sulfhydryl specifically. The details of the event are revealed by model synthetic studies and by kinetic, mass spectrometric, and crystallographic characterization.