Theoretical modelling of S-band thulium-doped silica fibre amplifiers

A comprehensive numerical model of a thulium-doped silica-based fibre amplifiers is presented. The model is spectrally and spatially resolved and is general in terms of pumping scheme used. The application of the model for predicting the S-band amplifier performance and for optimization of amplifier parameters is shown. For optimized Tm-doped fibre with ³H₄ level lifetime of 45 μs, which is the maximum value in the Tm-doped silica fibres prepared by the authors, above 20 dB of gain with 2000 mW pump power at the 1050 nm pump band can be expected according to the simulations.     

Direct identification of propargyl radical in combustion flames by vacuum ultraviolet photoionization mass spectrometry

We have developed an effusive laser photodissociation radical source, aiming for the production of vibrationally relaxed radicals. Employing this radical source, we have measured the vacuum ultraviolet (VUV) photoionization efficiency (PIE) spectrum of the propargyl radical (C(3)H(3)) formed by the 193 nm excimer laser photodissociation of propargyl chloride in the energy range of 8.5-9.9 eV using high-resolution (energy bandwidth = 1 meV) multibunch synchrotron radiation. The VUV-PIE spectrum of C(3)H(3) thus obtained is found to exhibit pronounced autoionization features, which are tentatively assigned as members of two vibrational progressions of C(3)H(3) in excited autoionizing Rydberg states. The ionization energy (IE = 8.674 +/- 0.001 eV) of C(3)H(3) determined by a small steplike feature resolved at the photoionization onset of the VUV-PIE spectrum is in excellent agreement with the IE value reported in a previous pulsed field ionization-photoelectron study. We have also calculated the Franck-Condon factors (FCFs) for the photoionization transitions C(3)H(3) (+)(X;nu(i),i = 1-12)<--C(3)H(3)(X). The comparison between the pattern of FCFs and the autoionization peaks resolved in the VUV-PIE spectrum of C(3)H(3) points to the conclusion that the resonance-enhanced autoionization mechanism is most likely responsible for the observation of pronounced autoionization features. We also present here the VUV-PIE spectra for the mass 39 ions observed in the VUV synchrotron-based photoionization mass spectrometric sampling of several premixed flames. The excellent agreement of the IE value and the pattern of autoionizing features of the VUV-PIE spectra observed in the photodissociation and flames studies has provided an unambiguous identification of the propargyl radical as an important intermediate in the premixed combustion flames. The discrepancy found between the PIE spectra obtained in flames and photodissociation at energies above the IE(C(3)H(3)) suggests that the PIE spectra obtained in flames might have contributions from the photoionization of vibrationally excited C(3)H(3) and/or the dissociative photoionization processes involving larger hydrocarbon species formed in flames.     

Temperature dependence of the surface anisotropy of Fe ultrathin films on Cu(001)

We report an experimental approach to separate temperature dependent reversible and irreversible contributions to the perpendicular magnetic anisotropy of Fe films grown at low temperatures on Cu(001) substrates. The surface anisotropy K(S)(T) is found to decrease linearly with temperature, causing a thermally induced spin reorientation into the plane. The irreversible shift of the spin reorientation transition and the coercivity of the iron films are directly correlated to the increasing Fe island size during annealing. The increased coercivity is discussed in terms of domain wall energy inhomogeneities provided by the islands.     

Erbium-doped twin-core fibre narrow-band filter for fibre lasers

Theoretical analysis of a recently experimentally demonstrated erbium-doped twin-core (ErTCF) fibre saturable-absorber-based narrow-band tracking filter is presented. Basic qualitative characteristics of the filter are deduced from an analogy with an ideally inhomogeneously broadened saturable absorber while the effect of wide band saturation of absorption due to spatial overlap of individual spectral components of the radiation is studied in detail using a numerical model based on coupled mode theory, resolved in space and frequency. The effect of the input power, twin-core fibre length and laser operating wavelength on the spectral characteristics of the filter is investigated.     

Explanation of appearance and characteristics of intermittency chaos of the impact oscillator

Chaotic motion of an intermittency type of the impact oscillator appears near segments of saddle-node stability boundaries of subharmonic motions with two different impacts in motion period, which is n multiple (n3) of excitation period. Chaotic motion arises due to an additional impact, which interrupts the process of instability. It is proved and shown by numerical simulations of the system motion. More detail characteristics of the intermittency chaos are evaluated. Described phenomena present a non-usual example, when transition cross special segments of saddle-node stability boundaries of subharmonic impact motions is reversible.     

Fast and efficient separation of immunoglobulin M from immunoglobulin G using short monolithic columns

Certain diagnostic, analytical and preparative applications require the separation of immunoglobulin G (IgG) from immunoglobulin M (IgM). In the present work, different ion-exchange methacrylate monoliths were tested for the separation of IgG and IgM. The strong anion-exchange column had the highest dynamic binding capacity reaching more than 20mg of IgM/ml of support. Additionally, separation of IgM from human serum albumin, a common contaminant in immunoglobulin purification, was achieved on the weak ethylenediamino anion-exchange column, which set the basis for the IgM purification method developed on convective interaction media (CIM) supports. Experiments also confirmed flow independent characteristics of the short monolithic columns.     

Technical Reports: Atoms to Aerosols—The Chemical Dynamics Beamline

Chemical dynamics is the study of the elementary processes and interactions in chemistry. Fundamental properties such as dipole moments, ionization energies, electron affinities, proton affinities, and electronic structure all contribute to the photochemistry, radiationless processes and reactivity underlying all physical processes. The making and breaking of chemical bonds, and the energy partitioning in chemical systems after transformation, are also in the domain of chemical dynamics.

The valence shell, the outermost shell of electrons in a system, contributes most to the physical properties of material. It is these electrons that are shared in covalent bonding, transferred in ionic systems, coupled to form bands in bulk material, and interact most strongly with the environment.     

Reversed phase monolithic analytical columns for the determination of HA1 subunit of influenza virus haemagglutinin

Monoliths are chromatographic stationary phases, which were specially designed for efficient purification of large biomolecules, like proteins, viruses and DNA. In this work, the small scale monolithic butyl (C4) and styrene-divinyl benzene (SDVB) columns were applied for reversed phase analyses of various degraded influenza viruses. The binding of the HA1 subunit of haemagglutinin to the monolithic columns was confirmed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and the Western blot. The working linear range was determined as 1.60 × 10¹⁰ viral particles/mL to at least 1.64 × 10¹¹ viral particles/mL, the limit of detection was found to be 2.56 × 10⁹ virus particles/mL and the limit of quantification was 5.12 × 10⁹ virus particles/mL. The analytical HPLC method developed with the H1N1 virus was also applicable for the analytics of the HA1 subunit of H3N2 influenza virus and the influenza B virus.     

Vacuum ultraviolet photoionization of C3

Photoionization efficiency (PIE) curves for C(3) molecules produced by laser ablation are measured from 11.0 to 13.5 eV with tunable vacuum ultraviolet undulator radiation. A step in the PIE curve versus photon energy, obtained with N(2) as the carrier gas, supports the conclusion of very effective cooling of C(3) to its linear (1)Sigma(g)(+) ground state. The second step observed in the PIE curve versus photon energy could be the first experimental evidence of the C(3)(+)((2)Sigma(g)(+)) excited state. The experimental results, complemented by ab initio calculations, suggest a state-to-state vertical ionization energy of 11.70 +/- 0.05 eV between the C(3)(X(1)Sigma(g)(+)) and the C(3)(+)(X(2)Sigma(u)(+)) states. An ionization energy of 11.61 +/- 0.07 eV between the neutral and ionic ground states of C(3) is deduced using the data together with our calculations. Accurate ab initio calculations are performed for both linear and bent geometries on the lowest doublet electronic states of C(3)(+) using Configuration Interaction (CI) approaches and large basis sets. These calculations confirm that C(3)(+) is bent in its electronic ground state, which is separated by a small potential barrier from the (2)Sigma(u)(+) minimum. The gradual increase at the onset of the PIE curve suggests a geometry change between the ground neutral and cationic states. The energies between several doublet states of the ion are theoretically determined to be 0.81, 1.49, and 1.98 eV between the (2)Sigma(u)(+) and the (2)Sigma(g)(+),( 2)Pi(u), (2)Pi(g) excited states of C(3)(+), respectively.     

Cr(VI) Oxidation of Cholesterol—A Kinetic Study Using N-Cetylpicolinium Dichromates,A Class of Novel Phase Transfer Oxidants

Kinetics and Catalysis - Kinetic study of cholesterol oxidation has been studied using a series of N-cetylpicolinium dichromates (CPDC), a class of phase transfer oxidants, in acetic acid medium...