The electronic absorption and magnetic circular dichroism spectra of IrBr6 2- in several host crystals

The absorption and magnetic circular dichroism (M.C.D.) spectrum of the IrBr₆ ^2- ion at room and liquid helium temperature has been studied in the host crystals (NH₄)₂SnBr₆, K₂SnBr₆ and (C₂H₅NH₃)₂SnBr₆ in the region ～11 000–21 000 cm^-1. An interpretation of the spectrum is presented which differs significantly from those suggested previously. In order of increasing energy the allowed bands are assigned to the following ligand-to-metal charge-transfer transitions: E_g ″(² T _2g )→ U_u ′(² T _1u ) (13–14 000 cm^-1), E_g ″(² T _2g )→ E_u ″(² T _2u ) (16 800 cm^-1), and E_g ″(² T _2g )→ U_u ′(² T _2u ) (～ 18 300 cm^-1). Both our absorption and M.C.D. data strongly suggest a Jahn-Teller splitting of the U_u ′(² T _1u ) state but contradict a previous suggestion of such a splitting of the U_u ′(² T _2u ) state. Consideration of σ—π mixing in the t _1u (π + σ) molecular orbital suggests that the ～17 300 cm^-1 band arises from the orbitally-forbidden E_g ″(² T _2g )→ E_u ′(² T _1u ) transition. Bands in the 11 000–13 000 cm^-1 region are assigned to parity-forbidden charge-transfer transitions to states generated by the t _1g (π)→ t _2g excitation. The fine structure seen at liquid helium temperature in K₂SnBr₆ : Ir⁴⁺ both in the 14 500 cm^-1 band and overlying the E_g ″→ U_u ′(² T _2u ) band appears to be associated with parity-forbidden transitions.     

Kinetic instabilities that limit β in the edge of a tokamak plasma: a picture of an H-mode pedestal

Plasma equilibria reconstructed from the Mega-Amp Spherical Tokamak have sufficient resolution to capture plasma evolution during the short period between edge-localized modes (ELMs). Immediately after the ELM, steep gradients in pressure, P, and density, n(e), form pedestals close to the separatrix, and they then expand into the core. Local gyrokinetic analysis over the ELM cycle reveals the dominant microinstabilities at perpendicular wavelengths of the order of the ion Larmor radius. These are kinetic ballooning modes in the pedestal and microtearing modes in the core close to the pedestal top. The evolving growth rate spectra, supported by gyrokinetic analysis using artificial local equilibrium scans, suggest a new physical picture for the formation and arrest of this pedestal.     

Peak Multiphoton Excitation of mCherry Using an Optical Parametric Oscillator (OPO)

mCherry is a red fluorescent protein which is bright, photostable, and has a low molecular weight. It is an attractive choice for multiphoton fluorescence imaging; however, the multiphoton excitation spectrum of mCherry is not known. In this paper we report the two photon excitation spectrum of mCherry measured up to 1190 nm in the near infrared (NIR) region. Skin tissues of transgenic mice that express mCherry were used in the experiments. mCherry in the tissues was excited with a Titanium:Sapphire laser and an optical parametric oscillator pumped by the Titanium:Sapphire laser. We found that the peak excitation of mCherry occurs at 1160 nm.     

C60 sputtering of organics: A study using TOF-SIMS, XPS and nanoindentation

Sputtering of organic materials using a C₆₀ primary ion beam has been demonstrated to produce significantly less accumulated damage compared to sputtering with monatomic and atomic-cluster ion beams. However, much about the dynamics of C₆₀ sputtering remains to be understood. We introduce data regarding the dynamics of C₆₀ sputtering by evaluating TOF-SIMS depth profiles of bulk poly(methyl methacrylate) (PMMA). Bulk PMMA provides an ideal test matrix with which to probe C₆₀ sputter dynamics because there is a region of steady-state secondary ion yield followed by irreversible signal degradation. C₆₀ sputtering of PMMA is evaluated as a function of incident ion kinetic energy using 10 keV C₆₀⁺, 20 keV C₆₀⁺ and 40 keV C₆₀⁺⁺ primary ions. Changes in PMMA chemistry, carbon accumulation and graphitization, and topography as a function of total C₆₀ ion dose at each accelerating potential is addressed.     

Fracto-emission accompanying adhesive failure in a model fiber pull-out system

Fracto-emission (FE) is the emission of particles and photons during and after fracture of materials. The observed emission includes electrons, negative and positive ions, neutral species in both ground states and in excited states, and visible photons. This emission can often serve as a sensitive probe of crack growth and may prove to be a useful tool for investigating molecular and microscopic events accompanying crack growth and for studying the details of failure modes in a variety of materials. Here, we examine photon and electron emission during failure of axially loaded stainless steel fixtures (e.g., rods) embedded in epoxy. These experimental data provide time resolved information on the sequence of events leading to interfacial fracture proceeding pullout. In addition, we examine the emissions during frictional pullout which over a large range of strain rates exhibits stick-slip behavior. Relations of these emissions to the fracture and pullout processes are discussed.     

On the exhaustivity of simplicial partitioning

During the last 40 years, simplicial partitioning has been shown to be highly useful, including in the field of nonlinear optimization, specifically global optimization. In this article, we consider results on the exhaustivity of simplicial partitioning schemes. We consider conjectures on this exhaustivity which seem at first glance to be true (two of which have been stated as true in published articles). However, we will provide counter-examples to these conjectures. We also provide a new simplicial partitioning scheme, which provides a lot of freedom, whilst guaranteeing exhaustivity.     

The role of photoelectronic processes in the formation of a fluorescent plume by 248-nm laser irradiation of single crystal NaNO3

 Visible fluorescent “plumes” are readily produced when nominally transparent ionic materials are exposed to pulsed UV laser irradiation. Over a wide range of laser fluences where plumes are observed, however, the photon and electron densities are inadequate to support multiphoton ionization and inverse bremsstrahlung, which are often used to explain plasma production and excitation of atomic spectral lines. We present evidence that the great majority of charged particles (electrons and positive ions) comprising the plume at the onset of formation in defect-laden NaNO₃ are emitted directly from the surface. A model is described wherein the required electron energy to excite and eventually ionize neutral atoms is provided by electrostatic interactions in the expanding plume. The time evolution of the “overlap” between the expanding charge cloud and thermally emitted neutrals accounts for the time evolution of the atomic line emissions after the laser pulse. Received: 15 August 1996/Accepted: 16 August 1996     

Thermal conductivity of noble gas + hydrogen mixtures: the separability of translational and internal energy transport

The Hirschfelder-Eucken assumption of an independent transport of translational and internal energy in gaseous noble gas + hydrogen mixtures is shown to be consistent with experimental thermal conductivity data for the binary systems Ne + H₂, Ne + D₂, Ar + H₂, Ar + D₂, Kr + H₂ and D₂.