Tracking ultrafast non-adiabatic dissociation dynamics of the deuterated water dication molecule.

We applied reaction microscopy to elucidate fast non-adiabatic dissociation dynamics of deuterated water molecules after direct photo-double ionization at 61 eV with synchrotron radiation. For the very rare D+ + O+ + D breakup channel, the particle momenta, angular, and energy distributions of electrons and ions, measured in coincidence, reveal distinct electronic dication states and their dissociation pathways via spin-orbit coupling and charge transfer at crossings and seams on the potential energy surfaces. Notably, we could distinguish between direct and fast sequential dissociation scenarios. For the latter case, our measurements reveal the geometry and orientation of the deuterated water molecule with respect to the polarization vector that leads to this rare 3-body molecular breakup channel. Aided by multi-reference configuration-interaction calculations, the dissociation dynamics could be traced on the relevant potential energy surfaces and particularly their crossings and seams. This approach also unraveled the ultrafast time scales governing these processes.

Contrasting Dynamics in Isoelectronic Anions Formed by Electron Attachment.

Cyanogen NCCN and cyanoacetylene HCCCN are isoelectronic molecules, and as such, they have many similar properties. We focus on the bond cleavage in these induced by the dissociative electron attachment. In both molecules, resonant electron attachment produces CN- with very similar energy dependence. We investigate the very different dissociation dynamics, in each of the two molecules, revealed by velocity map imaging of this common fragment. Different dynamics are manifested both in the excess energy partitioning and in the angular distributions of fragments. Based on the comparison with electron energy loss spectra, which provide information about possible parent states of the resonances (both optically allowed and forbidden excited states of the neutral target), we ascribe the observed effect to the distortion of the nuclear frame during the formation of core-excited resonance in cyanoacetylene. The proposed mechanism also explains a puzzling difference in the magnitude of the CN- cross section in the two molecules which has been so far unexplained.

Relativistic ultrafast electron diffraction at high repetition rates.

The ability to resolve the dynamics of matter on its native temporal and spatial scales constitutes a key challenge and convergent theme across chemistry, biology, and materials science. The last couple of decades have witnessed ultrafast electron diffraction (UED) emerge as one of the forefront techniques with the sensitivity to resolve atomic motions. Increasingly sophisticated UED instruments are being developed that are aimed at increasing the beam brightness in order to observe structural signatures, but so far they have been limited to low average current beams. Here, we present the technical design and capabilities of the HiRES (High Repetition-rate Electron Scattering) instrument, which blends relativistic electrons and high repetition rates to achieve orders of magnitude improvement in average beam current compared to the existing state-of-the-art instruments. The setup utilizes a novel electron source to deliver femtosecond duration electron pulses at up to MHz repetition rates for UED experiments. Instrument response function of sub-500 fs is demonstrated with < 100 fs time resolution targeted in future. We provide example cases of diffraction measurements on solid-state and gas-phase samples, including both micro- and nanodiffraction (featuring 100 nm beam size) modes, which showcase the potential of the instrument for novel UED experiments.

Efficiency of charge transfer in changing the dissociation dynamics of OD+ transients formed after the photo-fragmentation of D2O.

We present an investigation of the relaxation dynamics of deuterated water molecules after direct photo-double ionization at 61 eV. We focus on the very rare D+ + O+ + D reaction channel in which the sequential fragmentation mechanisms were found to dominate the dynamics. Aided by theory, the state-selective formation and breakup of the transient OD+(a1Δ, b1Σ+) is traced, and the most likely dissociation path-OD+: a1Δ or b1Σ+ → A 3Π â†’ X 3Σ- → B 3Σ--involving a combination of spin-orbit and non-adiabatic charge transfer transitions is determined. The multi-step transition probability of this complex transition sequence in the intermediate fragment ion is directly evaluated as a function of the energy of the transient OD+ above its lowest dissociation limit from the measured ratio of the D+ + O+ + D and competing D+ + D+ + O sequential fragmentation channels, which are measured simultaneously. Our coupled-channel time-dependent dynamics calculations reproduce the general trends of these multi-state relative transition rates toward the three-body fragmentation channels.

Atomic autoionization in the photo-dissociation of super-excited deuterated water molecules fragmenting into D+ + O+ + D.

We present the relaxation dynamics of deuterated water molecules via autoionization, initiated by the absorption of a 61 eV photon, producing the very rare D+ + O+ + D breakup channel. We employ the COLd target recoil ion momentum spectroscopy method to measure the 3D momenta of the ionic fragments and emitted electrons from the dissociating molecule in coincidence. We interpret the results using the potential energy surfaces extracted from multi-reference configuration interaction calculations. The measured particle energy distributions can be related to a super-excited monocationic state located above the double ionization threshold of D2O. The autoionized electron energy shows a sharp distribution centered around 0.5 eV, which is a signature of the atomic oxygen autoionization occurring in the direct and sequential dissociation processes of D2O+* at a large internuclear distance. In this way, an O+ radical fragment and a low-energy electron are created, both of which can trigger secondary reactions in their environment.

Selective bond-breaking in formic acid by dissociative electron attachment.

We report the results of a joint experimental and theoretical study of dissociative electron attachment to formic acid (HCOOH) in the 6-9 eV region, where H- fragment ions are a dominant product. Breaking of the C-H and O-H bonds is distinguished experimentally by deuteration of either site. We show that in this region H- ions can be produced by formation of two or possibly three Feshbach resonance (doubly-excited anion) states, one of which leads to either C-H or O-H bond scission, while the other can only produce formyloxyl radicals by O-H bond scission. Comparison of experimental and theoretical angular distributions of the anion fragment allows the elucidation of state specific pathways to dissociation.

Resonance signatures in the body-frame valence photoionization of CF4.

We present a combined experimental and theoretical investigation of the electron dynamics and body-frame angular dependence of valence photo-single ionization of CF4 and subsequent dissociation into CF3+ and F. Ionization from a valence t2 orbital shows overlapping shape resonances close to threshold that couple to the same total symmetry, leading to striking changes in the photoelectron angular distributions when viewed in the body-frame.

VUV and XUV reflectance of optically coated mirrors for selection of high harmonics.

We report the reflectance, ~1° from normal incidence, of six different mirrors as a function of photon energy, using monochromatic vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) radiation with energies between 7.5 eV and 24.5 eV. The mirrors examined included both single and multilayer optical coatings, as well as an uncoated substrate. We discuss the performance of each mirror, paying particular attention to the potential application of suppression and selection of high-order harmonics of a Ti:sapphire laser.

Time resolved 3D momentum imaging of ultrafast dynamics by coherent VUV-XUV radiation.

We present a new experimental setup for measuring ultrafast nuclear and electron dynamics of molecules after photo-excitation and ionization. We combine a high flux femtosecond vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) source with an internally cold molecular beam and a 3D momentum imaging particle spectrometer to measure electrons and ions in coincidence. We describe a variety of tools developed to perform pump-probe studies in the VUV-XUV spectrum and to modify and characterize the photon beam. First benchmark experiments are presented to demonstrate the capabilities of the system.

Correlation of Descriptive Analysis and Instrumental Puncture Testing of Watermelon Cultivars.

The textural properties of 5 seedless watermelon cultivars were assessed by descriptive analysis and the standard puncture test using a hollow probe with increased shearing properties. The use of descriptive analysis methodology was an effective means of quantifying watermelon sensory texture profiles for characterizing specific cultivars' characteristics. Of the 10 cultivars screened, 71% of the variation in the sensory attributes was measured using the 1st 2 principal components. Pairwise correlation of the hollow puncture probe and sensory parameters determined that initial slope, maximum force, and work after maximum force measurements all correlated well to the sensory attributes crisp and firm. These findings confirm that maximum force correlates well with not only firmness in watermelon, but crispness as well. The initial slope parameter also captures the sensory crispness of watermelon, but is not as practical to measure in the field as maximum force. The work after maximum force parameter is thought to reflect cellular arrangement and membrane integrity that in turn impact sensory firmness and crispness. Watermelon cultivar types were correctly predicted by puncture test measurements in heart tissue 87% of the time, although descriptive analysis was correct 54% of the time.

Signatures of bond formation and bond scission dynamics in dissociative electron attachment to methane.

We present a combined experimental and theoretical investigation of the dynamics and angular dependence of dissociative electron attachment to methane. We show that a triply degenerate (T2) Feshbach resonance is responsible for the broad 10 eV dissociation peak in methane. This resonance alone is shown to correlate asymptotically to the various dissociation channels observed experimentally. The molecular-frame entrance amplitude for electron attachment is calculated for each component of the threefold degenerate resonance. By investigating the topology of the anion potential energy surfaces, we deduce the main pathways to two- and three-body breakup channels involving both bond scission and bond formation. The computed fragment angular distributions reproduce the main trends of the experimental measurements.

Dynamics of the Dissociating Uracil Anion Following Resonant Electron Attachment.

We report a combined experimental and theoretical investigation of dissociative electron attachment (DEA) to the nucleobase uracil. Using ion momentum imaging experiments employing a DEA reaction microscope we have measured 3-dimensional momentum distributions of specific anionic fragments following DEA to uracil by 6 eV electrons. From the measured anion fragment kinetic energy we determine the possible dissociation pathways and the total kinetic energy release. We employ electronic structure and electron scattering calculations to determine the probability for electron attachment in the molecular frame. Combining these calculations with the imaging measurements, we reveal several key features of the coupled electronic and nuclear dynamics of DEA.

A momentum imaging microscope for dissociative electron attachment.

We describe an experimental approach to image the three-dimensional (3D) momentum distribution of the negative ions arising from dissociative electron attachment (DEA). The experimental apparatus employs a low energy pulsed electron gun, an effusive gas source and a 4π solid-angle ion momentum imaging spectrometer consisting of a pulsed ion extraction field, an electrostatic lens, and a time- and position-sensitive detector. The time-of-flight and impact position of each negative ion are measured event by event in order to image the full 3D ion momentum sphere. The system performance is tested by measuring the anion momentum distributions from two DEA resonances, namely H(-) from H(2)O(-) ((2)B(1)) and O(-) from O(2)(-) ((2)Π(u)). The results are compared with existing experimental and theoretical data.

Observation of threshold effects in positron scattering from the noble gases.

Channel coupling is a phenomenon that has been investigated for many scattering processes, and is responsible for the formation of cusps or steps in the cross sections for open scattering channels at, or near, the onset of a new scattering channel. It has long been speculated that the opening of the positronium formation channel may lead to the formation of such cusp features in the elastic positron scattering cross section. In this work, elastic scattering of positrons has been measured in the region of the positronium formation threshold for the noble gases He-Xe. Cusplike behavior is observed and, while the features which are observed appear broad, they represent a magnitude of between 4 and 15% of the total elastic cross section. No evidence is found of any other features in this region, at least within the uncertainty of the present data, discounting the possibility of scattering resonances.

Microscopic quantification of cell integrity in raw and processed onion parenchyma cells.

UNLABELLED: A cell viability assessment method based computer vision analysis of the uptake of neutral red dye was used to quantify cell membrane integrity in raw and processed parenchyma cells of onion tissues. The presence of stained vacuoles was used as an indicator of tonoplast membrane integrity and photomicrographs were acquired for microscopic image analysis and cell integrity quantification. Two different image analysis methods, involving the analysis of the saturation and green components of RGB (red, green, blue) images, were compared to the conventional cell count method. Use of the saturation component of RGB images allowed for the visualization and quantification of viable and inviable cells as well as extracellular air spaces. The combination of neutral red uptake, as visualization by light field microscopy, and saturation image analysis, allowed for quantitative determination of the effects of high pressure processing on onion cell integrity. PRACTICAL APPLICATION: Preservation of vegetable tissues may involve heating or other methods that result in the loss of tissue integrity and potentially quality deterioration. In this study, we stained unprocessed and processed onion tissues with neutral red dye and then used a microscope and a computer imaging program to quantify how many cells were intact or ruptured.

Influence of cell integrity on textural properties of raw, high pressure, and thermally processed onions.

UNLABELLED: The integrity of onion cells and its impact on tissue texture after high pressure and thermal processing was studied. The contribution of cell membranes and the pectic component of cell walls on the texture properties of onion tissue were analyzed. Neutral red (NR) staining of onion parenchyma cell vacuoles was used for the evaluation of cell membrane integrity and microscopic image analysis was used for its quantification. The content of methanol in tissue as a result of pectin methylesterase activity was used to evaluate the pectin component of the middle lamella and cell walls and the hardening effect on the tissue after processing. High pressure treatments consisted of 5-min holding times at 50, 100, 200, 300, or 600 MPa. Thermal treatments consisted of 30-min water bath exposure to 40, 50, 60, 70, or 90 °C. In the high pressure treatments, loss of membrane integrity commenced at 200 MPa and total loss of membrane integrity occurred at 300 MPa and above. In the thermal treatments, membrane integrity was lost between 50 and 60 °C. The texture of onions was influenced by the state of the membranes and texture profiles were abruptly modified once membrane integrity was lost. Hardening of the tissue corresponded with pressure and temperature PME activation and occurred after membrane integrity loss. PRACTICAL APPLICATION: The texture of vegetables is an important quality attribute that affects consumer preference. Loss of textural integrity also indicates that other biochemical reactions that affect color, flavor, and nutrient content may occur more rapidly. In this study, we analyzed changes in the texture of onions after preservation with heat and high pressure.

The Radiation Injury Severity Classification system: an early injury assessment tool for the frontline health-care provider.

Our goal was to adapt current diagnostic methods for radiation overexposure patients into a practical system that can be implemented rapidly and reliably by responders unfamiliar with the effects of radiation. Our Radiation Injury Severity Classification (RISC) system uses clinical and haematological parameters from the prodromal phase of the acute radiation syndrome (ARS) to classify acute radiation injury for purposes of managing treatment disposition. Data from well-documented ARS cases were used to test the RISC system. Three-day summaries were generated for each case. These were individually reviewed by the three physicians most involved with the development of the system to establish both a consensus case score (CCS) and disposition category ranges. 30 volunteer raters from varying health disciplines using the RISC system then each independently rated a random selection of 12 cases for injury severity in a self-trained field-simulation exercise. The CCS identified discrete cut-off ranges for the three disposition categories in both manageable and mass casualty events. The group of raters, after a modest period of self-training, achieved overall levels of pairwise agreement with the CCS category of 0.944 for manageable events and 0.947 for mass casualty situations. In conclusion, an early assessment of the severity of the ARS injury is required for an appropriate disposition determination. The RISC system should produce reasonably accurate and reliable assessments of radiation injury severity within 6-12 hours post exposure despite the probable absence of physical dosimetric data.

Uncertainties analysis of doses resulting from chronic inhalation of plutonium at the Mayak production association.

A method is presented to determine the uncertainties in the reported dose due to incorporated plutonium for the Mayak Worker Cohort. The methodology includes errors generated by both detection methods and modeling methods. To accomplish the task, the method includes classical statistics, Monte Carlo, perturbation, and reliability groupings. Uncertainties are reported in percent of reported dose as a function of total body burden. The cohort was initially sorted into six reliability groups, with "A" being the data set that the investigators are most confident is correct and "G" being the data set with the most ambiguous data. Categories were adjusted based on preliminary calculation of uncertainties using the sorting criteria. Specifically, the impact of transportability (the parameter used to describe the transport of plutonium from the lung to systemic organs) was underestimated, and the structure of the sort was reorganized to reflect the impact of transportability. The finalized categories are designated with Roman numerals I through V, with "I" being the most reliable. Excluding Category V (neither bioassay nor autopsy), the highest uncertainty in lung doses is for individuals from Category IV-which ranged from 90-375% for total body burdens greater than 10 Bq, along with work histories that indicated exposure to more than one transportability class. The smallest estimated uncertainties for lung doses were determined by autopsy. Category I has a 32-38% uncertainty in the lung dose for total body burdens greater than 1 Bq. First, these results provide a further definition and characterization of the cohort and, second, they provide uncertainty estimates for these plutonium exposure categories.

Antibiotic resistance in coagulase-negative staphylococci isolated from Cope's gray treefrogs (Hyla chrysoscelis).

Organisms belonging to the genus Staphylococcus were isolated on mannitol salt agar from the feces of wild caught Cope's gray treefrogs (Hyla chrysoscelis) from east-central Kansas. All 222 presumptive isolates were confirmed as coagulase-negative staphylococci with Staphylococcus sciuri and Staphylococcus xylosus being most prevalent. Antibiotic susceptibility patterns to five different antibiotics were determined and the results indicated 99% of all isolates were resistant to penicillin G and 59% of the isolates were resistant to oxacillin, a clinical substitute for methicillin. Due to the significance of methicillin resistance in the genus Staphylococcus, 10 randomly chosen oxacillin resistant organisms were analyzed for the presence of the mecA gene, which is known to code for methicillin resistance. The gene was detected in four of the 10 organisms examined. These data indicate that gray treefrogs are harboring inordinately large numbers of methicillin resistant staphylococci as part of their normal flora and that the mechanism of methicillin resistance may be independent of mecA.

The potential for CYP2D6 inhibition screening using a novel scintillation proximity assay-based approach.

High throughput inhibition screens for human cytochrome P450s (CYPs) are being used in preclinical drug metabolism to support drug discovery programs. The versatility of scintillation proximity assay (SPA) technology has enabled the development of a homogeneous high throughput assay for cytochrome P450 2D6 (CYP2D6) inhibition screen using [O-methyl-(14)C]dextromethorphan as substrate. The basis of the assay was the trapping of the O-demethylation product, [(14)C]HCHO, on SPA beads. Enzyme kinetics parameters V(max) and apparent K(m), determined using pooled human liver microsomes and microsomes from baculovirus cells coexpressing human CYP2D6 and NADPH-cytochrome P450 reductase, were 245 pmol [(14)C]HCHO/min/mg protein and 11 microM, and 27 pmol [(14)C]HCHO/min/pmol and 1.6 microM, respectively. In incubations containing either pooled microsomes or recombinant CYP2D6, [(14)C]dextromethorphan O-demethylase activity was inhibited in the presence of quinidine (IC(50) = 1.0 microM and 20 nM, respectively). By comparison, inhibitors selective for other CYP isoforms were relatively weak (IC(50) > 25 microM). In agreement, a selective CYP2D6 inhibitory monoclonal antibody caused greater than 90% inhibition of [(14)C]dextromethorphan O-demethylase activity in human liver microsomes, whereas CYP2C9/19- and CYP3A4/5-selective antibodies elicited a minimal inhibitory effect. SPA-based [(14)C]dextromethorphan O-demethylase activity was also shown to correlate (r(2) = 0.6) with dextromethorphan O-demethylase measured by high-performance liquid chromatography in a bank of human liver microsomes (N = 15 different organ donors). In a series of known CYP2D6 inhibitors/substrates, the SPA-based assay resolved potent inhibitors (IC(50) < 2 microM) from weak inhibitors (IC(50) >or= 20 microM). It is concluded that the SPA-based assay described herein is suitable for CYP2D6 inhibition screening using either native human liver microsomes or cDNA-expressed CYP2D6.