Characterization of the drastic increase in molecular mobility of a deformed amorphous polymer

Original experiments of dynamic mechanical analysis and small angle x-ray scattering on a deformed amorphous polymer below its glass transition temperature are reported. The mechanical treatment reveals high mobility zones induced by shearing and leads to a drastic increase in the molecular mobility of the system. These domains are evidenced by small angle x-ray scattering measurements, and their geometrical characteristics are independent of the applied deformation. An experimental procedure is proposed to determine an apparent activation energy associated with high mobility domains. The energy values obtained for intermediate modes rise from the beta to the alpha relaxation ones.     

Challenges encountered in extending the sensitivity of US Environmental Protection Agency Method 314.0 for perchlorate in drinking water

Concerns about the potential adverse health effects of perchlorate at concentrations below the minimum reporting level (MRL) of US Environmental Protection Agency (EPA) Method 314.0 (generally recognized as 4.0 microg/l) have led to an interest in increasing the sensitivity of the method. This work describes the use of 2 mm columns with a large-loop direct injection method, a column concentration technique and this concentration technique with a background reduction step, to increase the sensitivity for the analysis of trace levels of perchlorate in high ionic strength matrices. The concentrator columns studied were the Dionex TAC LP-1 and a new Dionex high capacity Cryptand concentrator column. The use of a surrogate to monitor trapping efficiency for the concentration technique and the use of confirmational columns to minimize the potential for false positives are also discussed. The large-loop direct injection method and the column concentration methods provided acceptable data when the samples were pre-treated with solid phase pretreatment cartridges. The background reduction technique did not provide acceptable data with either of the concentrator columns evaluated.     

Internal energy content of n-butylbenzene, bromobenzene, iodobenzene and aniline molecular ions generated by two-photon ionization at 266 nm. A photodissociation study

A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd.     

The fixed-point algebra of tensor-product actions of finite Abelian groups on UHF-algebras

Let G be a finite Abelian group acting by tensor-product automorphisms on a UHF-C¹-algebra $\text{D}$. Extending a result of A. Kishimoto it is shown that the number of extremal traces on the fixed-point algebra $\text{D}$^G equals the cardinality of the subgroup K of automorphisms in G which are weakly inner in the trace representation of $\text{D}$.     

Spectrum of light scattered from viscoelastic gels

Spectra of polarized light scattered from model networks of polystyrene swollen by benzene have been measured by optical mixing spectroscopy. Various series of networks of different functionalities and different lengths of the elastic chain elements have been investigated. A theoretical expression for the characteristic time constant of fluctuations has been derived from rubber elasticity theory. An analysis of the experimental results within the framework of this theory allows determination of the frictional constants of the gels.     

Improved output power performance of a phase conjugated laser oscillator

A method for increasing the output power of a phase conjugated oscillator (PCO) by using two stimulated-Brillouin-scattering (SBS) cells is described. The average power has been more than doubled and the peak power has been increased by twenty times compared to the single-SBS-cell PCO. Near unity beam quality has been measured.     

The neuroblast and angioblast chemotaxic factor SDF-1 (CXCL12) expression is briefly up regulated by reactive astrocytes in brain following neonatal hypoxic-ischemic injury

Background  

Stromal cell-derived factor 1 (SDF-1 or CXCL12) is chemotaxic for CXCR4 expressing bone marrow-derived cells. It functions in brain embryonic development and in response to ischemic injury in helping guide neuroblast migration and vasculogenesis. In experimental adult stroke models SDF-1 is expressed perivascularly in the injured region up to 30 days after the injury, suggesting it could be a therapeutic target for tissue repair strategies. We hypothesized that SDF-1 would be expressed in similar temporal and spatial patterns following hypoxic-ischemic (HI) injury in neonatal brain.