Interlaboratory ring test of time-resolved fluoroimmunoassays for zeranol and alpha-zearalenol and comparison with zeranol test kits

Many zeranol immunoassay test kits cross-react with toxins formed by naturally occurring Fusarium spp. fungi, leading to false-positive screening results. This paper describes the evaluation and application of recently published, dry reagent time-resolved fluoroimmunoassays (TR-FIA) for zeranol and the toxin alpha-zearalenol. A ring test of bovine urine fortified with zeranol and/or alpha-zearalenol in four European Union National Reference Laboratories demonstrated that the TR-FIA tests were accurate and robust. The alpha-zearalenol TR-FIA satisfactorily quantified alpha-zearalenol in urine fortified at 10-30 ng ml(-1) . The specificity-enhanced zeranol TR-FIA accurately quantified zeranol in the range 2-5 ng ml(-1) and gave no false-positive results in blank urine, even in the presence of 30 ng ml(-1) alpha-zearalenol. Zeranol TR-FIA specificity was demonstrated further by analysing incurred zeranol-free urine samples containing natural Fusarium spp. toxins. The TR-FIA yielded no false-positive results in the presence of up to 22 ng ml(-1) toxins. The performance of four commercially available zeranol immunoassay test kits was more variable. Three kits produced many false-positive results. One kit produced only one potential false-positive using a protocol that was longer than that of the TR-FIA. These TR-FIAs will be valuable tools to develop inspection criteria to distinguish illegal zeranol abuse from contamination arising from in vivo metabolism of Fusarium spp. toxins.

A time-resolved immunoassay to measure serum antibodies to the rotavirus VP6 capsid protein

The rotavirus (RV) inner capsid protein VP6 is widely used to evaluate immune response during natural infection and in vaccine studies. Recombinant VP6 from the most prevalent circulating rotavirus strains in each subgroup (SG) identified in a birth cohort of children in southern India [SGII (G1P[8]) and SGI (G10P[11])] were produced. The purified proteins were used to measure VP6-specific antibodies in a Dissociation-Enhanced Lanthanide Fluorometric Immunoassay (DELFIA). The ability of the assay to detect a =2 fold rise in IgG level in a panel of serum samples from a longitudinal study was compared to a gold standard virus-capture ELISA. A strong association was observed between the assays (p

Serological responses to experimental Norwalk virus infection measured using a quantitative duplex time-resolved fluorescence immunoassay

A quantitative duplex time-resolved fluorescence assay, dissociation-enhanced lanthanide fluorescent immunoassay (DELFIA), was developed to measure Norwalk virus (NV)-specific IgA and IgG antibodies simultaneously. The duplex assay showed superior performance by detecting seroconversion following experimental NV infection at an earlier time point than a reference total immunoglobulin enzyme-linked immunosorbent assay (ELISA).

Time-Resolved Characterization of the Formation of a Collisionless Shock

We report on the temporally and spatially resolved detection of the precursory stages that lead to the formation of an unmagnetized, supercritical collisionless shock in a laser-driven laboratory experiment. The measured evolution of the electrostatic potential associated with the shock unveils the transition from a current free double layer into a symmetric shock structure, stabilized by ion reflection at the shock front. Supported by a matching particle-in-cell simulation and theoretical considerations, we suggest that this process is analogous to ion reflection at supercritical collisionless shocks in supernova remnants.

Time-Resolved DRIFTS, MS, and Resistance Study of SnO2 Materials: The Role of Surface Hydroxyl Groups in Formation of Donor States

Time-resolved DRIFTS, MS, and resistance measurements were used to study the interaction of undoped and Pd-doped SnO2 with H-2 in air and argon at 300 degrees C. Using first-order kinetics, we compare the time constants for the resistance drop and its partial recovery with those of the surface hydroxyl evolution and water formation in the gas phase upon exposure to hydrogen. In the case of the undoped oxide, resistance and bridging hydroxyls (BOHs) evolve similarly, manifesting a fast main drop followed by recovery at a similar rate. The rate of water formation for this material was found to be much slower than that of the main drop in both the resistance and BOHs. In contrast, the resistance change for SnO2-Pd appeared to be similar to that of water formation, and no correlation was found between the evolution of resistance and surface OHs. Isotopic exchange on both materials revealed that water formation occurs via fast and slow hydrogen transfer to surface oxygen species. While the former originates from just-adsorbed hydrogen, the latter appears to proceed from the preadsorbed OHs. Both surfaces exhibit close interaction between chemisorbed oxygen and existing bridging OH groups, indicating that the latter is an intermediate in the hydrogen oxidation and generation of donor states on the surface.

Time-resolved four-wave-mixing spectroscopy for inner-valence transitions

Noncollinear four-wave-mixing (FWM) techniques at near-infrared (NIR), visible, and ultraviolet frequencies have been widely used to map vibrational and electronic couplings, typically in complex molecules. However, correlations between spatially localized inner-valence transitions among different sites of a molecule in the extreme ultraviolet (XUV) spectral range have not been observed yet. As an experimental step toward this goal, we perform time-resolved FWM spectroscopy with femtosecond NIR and attosecond XUV pulses. The first two pulses (XUV-NIR) coincide in time and act as coherent excitation fields, while the third pulse (NIR) acts as a probe. As a first application, we show how coupling dynamics between odd- and even-parity, inner-valence excited states of neon can be revealed using a two-dimensional spectral representation. Experimentally obtained results are found to be in good agreement with ab initio time-dependent R-matrix calculations providing the full description of multielectron interactions, as well as few-level model simulations. Future applications of this method also include site-specific probing of electronic processes in molecules.

Time-resolved dosimetric verification of respiratory-gated radiotherapy exposures using a high-resolution 2D ionisation chamber array

The aim of this work was to track and verify the delivery of respiratory-gated irradiations, performed with three versions of TrueBeam linac, using a novel phantom arrangement that combined the OCTAVIUS® SRS 1000 array with a moving platform. The platform was programmed to generate sinusoidal motion of the array. This motion was tracked using the real-time position management (RPM) system and four amplitude gating options were employed to interrupt MV beam delivery when the platform was not located within set limits. Time-resolved spatial information extracted from analysis of x-ray fluences measured by the array was compared to the programmed motion of the platform and to the trace recorded by the RPM system during the delivery of the x-ray field. Temporal data recorded by the phantom and the RPM system were validated against trajectory log files, recorded by the linac during the irradiation, as well as oscilloscope waveforms recorded from the linac target signal. Gamma analysis was employed to compare time-integrated 2D x-ray dose fluences with theoretical fluences derived from the probability density function for each of the gating settings applied, where gamma criteria of 2%/2 mm, 1%/1 mm and 0.5%/0.5 mm were used to evaluate the limitations of the RPM system. Excellent agreement was observed in the analysis of spatial information extracted from the SRS 1000 array measurements. Comparisons of the average platform position with the expected position indicated absolute deviations of  <0.5 mm for all four gating settings. Differences were observed when comparing time-resolved beam-on data stored in the RPM files and trajectory logs to the true target signal waveforms. Trajectory log files underestimated the cycle time between consecutive beam-on windows by 10.0  ±  0.8 ms. All measured fluences achieved 100% pass-rates using gamma criteria of 2%/2 mm and 50% of the fluences achieved pass-rates  >90% when criteria of 0.5%/0.5 mm were used. Results using this novel phantom arrangement indicate that the RPM system is capable of accurately gating x-ray exposure during the delivery of a fixed-field treatment beam.

A new look at the pulsating DB white dwarf GD 358: Line-of-sight velocity measurements and constraints on model atmospheres

We report on our findings of the bright, pulsating, helium atmosphere white dwarf GD 358, based on time-resolved optical spectrophotometry. We identify 5 real pulsation modes and at least 6 combination modes at frequencies consistent with those found in previous observations. The measured Doppler shifts from our spectra show variations with amplitudes of up to 5.5 km s-1 at the frequencies inferred from the flux variations. We conclude that these are variations in the line-of-sight velocities associated with the pulsational motion. We use the observed flux and velocity amplitudes and phases to test theoretical predictions within the convective driving framework, and compare these with similar observations of the hydrogen atmosphere white dwarf pulsators (DAVs). The wavelength dependence of the fractional pulsation amplitudes (chromatic amplitudes) allows us to conclude that all five real modes share the same spherical degree, most likely, l=1. This is consistent with previous identifications based solely on photometry. We find that a high signal-to-noise mean spectrum on its own is not enough to determine the atmospheric parameters and that there are small but significant discrepancies between the observations and model atmospheres. The source of these remains to be identified. While we infer Teff =24 kK and log g ~ 8.0 from the mean spectrum, the chromatic amplitudes, which are a measure of the derivative of the flux with respect to the temperature, unambiguously favour a higher effective temperature, 27 kK, which is more in line with independent determinations from ultra-violet spectra.

Observing time-dependent vibrational quantum dynamics in deuterium hydride molecular ions

Few-cycle laser pulses are used to "pump and probe" image the vibrational wavepacket dynamics of a HD+ molecular ion. The quantum dephasing and revival structure of the wavepacket are mapped experimentally with time-resolved photodissociation imaging. The motion of the molecule is simulated using a quantum-mechanical model predicting the observed structure. The coherence of the wavepacket is controlled by varying the duration of the intense laser pulses. By means of a Fourier transform analysis both the periodicity and relative population of the vibrational states of the excited molecular ion have been characterized.

Wide angle crystal spectrometer for angularly and spectrally resolved x-ray scattering experiments

A novel wide angle spectrometer has been implemented with a highly oriented pyrolytic graphite crystal coupled to an image plate. This spectrometer has allowed us to look at the energy resolved spectrum of scattered x rays from a dense plasma over a wide range of angles ( ~ 30°) in a single shot. Using this spectrometer we were able to observe the temporal evolution of the angular scatter cross section from a laser shocked foil. A spectrometer of this type may also be useful in investigations of x-ray line transfer from laser-plasmas experiments.

A puzzling periodicity in the pulsating DA white dwarf G 117-B15A

We present time-resolved optical spectrophotometry of the pulsating hydrogen atmosphere (DA) white dwarf G 117-B15A. We find three periodicities in the pulsation spectrum (215 s, 272 s, and 304 s) all of which have been found in earlier studies. By comparing the fractional wavelength dependence of the pulsation amplitudes ( chromatic amplitudes) with models, we confirm a previous report that the strongest mode, at 215 s, has l = 1. The chromatic amplitude for the 272 s mode is very puzzling, showing an increase in fractional amplitude with wavelength that cannot be reproduced by the models for any ` at optical wavelengths. Based on archival HST data, we show that while the behaviour of the 215 s mode at ultra-violet wavelengths is as expected from models, the weird behaviour of the 272 s periodicity is not restricted to optical wavelengths in that it fails to show the expected increase in fractional amplitude towards shorter wavelengths. We discuss possible causes for the discrepancies found for the 272 s variation, but find that all are lacking, and conclude that the nature of this periodicity remains unclear.

RESONANCE RAMAN-SPECTRA OF THE TRIPLET-STATE OF FREE-BASE TETRAPHENYLPORPHYRIN AND 6 OF ITS ISOTOPOMERS

The resonance Raman spectra of the ground state and the lowest excited tripler state of free-base tetraphenylporphyrin and six of its isotopomers have been obtained using two-color time-resolved techniques. Ground-state spectra were recorded using low-energy 447 nm probe laser pulses, and triplet-state spectra were probed, with similar pulses, 30 ns after high-energy excitation with 532 nm pump pulses. Polarization data on both the ground and triplet states are also reported. The resonance Raman spectrum of the triplet is very different from that of the ground state but the combination of extensive isotope substitution with polarization data allows bands in the ground state to be assigned and corresponding bands in the tripler state to be located. Isotope shifts of the same bands in the S-0 and T-1 states are similar, implying that the compositions of the vibrational modes do not change significantly on excitation. Two of the strongest bands in the T-1 spectra are associated with phenyl ring substituents; these are shifted less than 5 cm(-1) between the S-0 and T-1 states so that bonding in the phenyl substituents is barely affected by excitation to the T-1 state. The changes in position of the porphyrin ring bands are larger, but still only tens of cm(-1) or less, the main changes in the spectra being due to differences in relative band intensities in the two states. The relatively small shifts in the porphyrin ring band positions which are observed show that the excitation energy is not localized on a single small region of the molecule but is delocalized over the entire porphyrin skeleton. This picture of an excited species with high chemical reactivity, but with individual bonds only slightly perturbed from the ground state, is contrasted with molecules, such as benzophenone, where excitation causes a large perturbation in the bonding within a single functional group.

TEMPORALLY AND SPATIALLY-RESOLVED PLASMA PARAMETERS AND EEDF MEASUREMENTS IN A LOW-FREQUENCY DISCHARGE

A time-resolved Langmuir probe technique is used to measure the dependence of the electron density, electron temperature, plasma potential and electron energy distribution function (EEDF) on the phase of the driving voltage in a RF driven parallel plate discharge. The measurements were made in a low-frequency (100-500 kHz), symmetrically driven, radio frequency discharge operating in H-2, D-2 and Ar at gas pressures of a few hundred millitorr. The EEDFs could not be represented by a single Maxwellian distribution and resembled the time averaged EEDFs reported in 13.56 MHz discharges. The measured parameters showed structure in their spatial and temporal dependence, generally consistent with a simple oscillating sheath model. Electron temperatures of less than 0.1 eV were measured during the phase of the RF cycle when both electrodes are negative with respect to the plasma.

The VLT-FLAMES Tarantula survey: XX. The nature of the X-ray bright emission-line star VFTS 399

Context: The stellar population of the 30 Doradus star-forming region in the Large Magellanic Cloud contains a subset of apparently single, rapidly rotating O-type stars. The physical processes leading to the formation of this cohort are currently uncertain. 

Aims: One member of this group, the late O-type star VFTS 399, is found to be unexpectedly X-ray bright for its bolometric luminosity-in this study we aim to determine its physical nature and the cause of this behaviour. 

Methods: To accomplish this we performed a time-resolved analysis of optical, infrared and X-ray observations. 

Results: We found VFTS 399 to be an aperiodic photometric variable with an apparent near-IR excess. Its optical spectrum demonstrates complex emission profiles in the lower Balmer series and select He i lines-taken together these suggest an OeBe classification. The highly variable X-ray luminosity is too great to be produced by a single star, while the hard, non-thermal nature suggests the presence of an accreting relativistic companion. Finally, the detection of periodic modulation of the X-ray lightcurve is most naturally explained under the assumption that the accretor is a neutron star. 

Conclusions: VFTS 399 appears to be the first high-mass X-ray binary identified within 30 Dor, sharing many observational characteristics with classical Be X-ray binaries. Comparison of the current properties of VFTS 399 to binary-evolution models suggests a progenitor mass 25 M_⊙ for the putative neutron star, which may host a magnetic field comparable in strength to those of magnetars. VFTS 399 is now the second member of the cohort of rapidly rotating "single" O-type stars in 30 Dor to show evidence of binary interaction resulting in spin-up, suggesting that this may be a viable evolutionary pathway for the formation of a subset of this stellar population.