Measurements of absolute, single charge-exchange cross sections of H+, He+ and He2+ with H2O and CO2

Absolute measurements have been made of single-electron charge-exchange cross sections of H+, He+, and He2+ in H2O and CO2 in the energy range 0.3-7.5 keV amu(-1). Collisions of this type occur in the interaction of solar wind ions with cometary gases and have been observed by the Giotto spacecraft using the Ion Mass Spectrometer/High Energy Range Spectrometer (IMS/HERS) during a close encounter with comet Halley in 1986. Increases in the He+ ion density, and in the He2+ to H+ density ratio were reported by Shelley et al, and Fuselier et al. and were explained by charge exchange. However, the lack of reliable cross sections for this process made interpretation of the data difficult. New cross sections are presented and discussed in relation to the Giotto observations.

Influence of solution viscosity and injection protocol on distribution patterns of jet injectors: Application to photodynamic tumour targeting

Photodynamic therapy of deep or nodular skin tumours is currently limited by the poor tissue penetration of the porphyrin precursor 5-aminolevulinic acid (ALA) and preformed photosensitisers. In this study, we investigated the potential of jet injection to deliver both ALA and a preformed photosensitiser (meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate, TMP) into a defined volume of skin. Initial studies using a model hydrogel showed that as standoff distance is increased, injection depth decreases. As the ejected volume is increased, injection depth increases. It was also shown, for the first time, that, as injection solution viscosity was increased, for a given injection setting and standoff distance, both total depth of jet penetration, L-t, and depth at which the maximum width of the penetration pattern occurred, L-m, decreased progressively. For a standoff distance of zero, the maximum width of the penetration pattern, L-w, increased progressively with increasing viscosity at each of the injection settings. Conversely, when the standoff distance was 2.5 mm, L-w decreased progressively with increasing viscosity. Studies with neonate porcine skin revealed that an injection protocol comprising an 8.98 mPas solution, an arbitrary injection setting of 8 and a standoff distance of zero was capable of delivering photosensitisers to a volume of tissue (L-t of 2.91 mm, L-m of 2.14 mm, L-w of 5. 10 mm) comparable to that occupied by a typical nodular basal cell carcinoma. Both ALA and TMP were successfully delivered using jet injection, with peak tissue concentrations (67.3 mg cm(-3) and 5.6 mg cm(-3), respectively) achieved at a depth of around 1.0 mm and substantial reductions in drug concentration seen at depths below 3.0 mm. Consequently, jet injection may be suitable for selective targeting of ALA or preformed photosensitisers to skin tumours. (c) 2007 Elsevier B.V. All rights reserved.

Validating Injection Stretch-Blow Molding Simulation Through Free Blow Trials

A 2D isothermal finite element simulation of the injection stretch-blow molding (ISBM) process for polyethylene terephthalate (PET) containers has been developed through the commercial finite element package ABAQUS/standard. In this work, the blowing air to inflate the PET preform was modeled through two different approaches: a direct pressure input (as measured in the blowing machine) and a constant mass flow rate input (based on a pressure-volume-time relationship). The results from these two approaches were validated against free blow and free stretch-blow experiments, which were instrumented and monitored through high-speed video. Results show that simulation using a constant mass flow rate approach gave a better prediction of volume vs. time curve and preform shape evolution when compared with the direct pressure approach and hence is more appropriate in modeling the preblowing stage in the injection stretch-blow molding process

Self-potential signatures associated with an injection experiment at an in situ biological permeable reactive barrier

Strategies available to evaluate the performance of in situ permeable reactive barriers are currently not well developed and often rely on fluid and media sampling directly from the permeable reactive barrier (PRB). Here, we investigate the utility of the self-potential (SP) method as a technique to monitor in situ PRB performance. Our field study was conducted at in situ biological PRB in Portadown, Northern Ireland, UK, which was emplaced to assist in the remediation of groundwater contamination (e.g., hydrocarbons, ammonia) that resulted from the operations and waste disposal practices of a former gasworks. Borehole SP measurements were collected during the injection of contaminant groundwater slugs in an attempt to monitor/detect the response of the microbial activity associated with the breakdown of the added contaminants into the PRB. In addition, an uncontaminated groundwater slug was injected into a different portion of the PRB as a ‘control’ and SP measurements were collected for comparison to the SP response of the contaminant slugs. The results of the SP signals due to the contaminant injections show that the magnitude of the response was relatively small (<10 mV) yet showed a consistent decrease during both contaminant injections. The net decrease in SP recorded during the contaminant injections slowly rebounded to near background values through ~44 hours post-injection. The SP response during the uncontaminated injection showed a slight, albeit negligible (within the margin of error), 1 mV increase in the measured SP signals, in contrast to the contaminant injections. The results of the SP signals recorded from the uncontaminated groundwater injection also persisted through a period of ~47 hours after injection but show a net increase in SP relative to pre-injection values. Based on the difference in SP response between the contaminated and uncontaminated injections, we suggest that the responses are likely to be the result of differences in the chemistry of the injection types (contaminated versus uncontaminated) and in situ groundwater. We argue that the SP signals associated with the contaminated injections are dominated by diffusion (electrochemical) potential, possibly enhanced by a microbial effect. While the results of our investigation show a consistent SP response associated with the contaminant injections that is dominated by diffusional effects, further studies are required in order to better understand the effect of microbial activity on SP signals and the potential utility for the SP method to detect/monitor changes that may be indicative of biological PRB performance.

Solid and liquid charge-transfer complex formation between 1-methylnaphthalene and 1-alkyl-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide ionic liquids

Liquid charge-transfer (CT) complexes were observed to form on contacting electron-rich aromatics with electron withdrawing group appended 1-alkyl-4-cyanopyridinium ionic liquids (ILs). Cooling below the melting point of the ionic liquid resulted in crystallisation of ionic liquid from the complex for 2-cyano and 3-cyano pyridinium isomers and in the formation of a 1 : 1 IL : aromatic crystalline CT-complex with the 4-cyanopyridinium isomer. The liquid structure of a 1 : 1 mixture of 1-methyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl} imide with 1-methylnaphthalene has been probed by neutron diffraction experiments and molecular dynamics simulations. A high degree of correlation between the experimental data and the simulations was found with a significant displacement of the anions from around the cation by the aromatic species and the resulting structure having pi-pi stacks between the cations and the aromatic.

Numerical simulation of the charge balance and temperature evolution in an electron beam ion trap

A computer code has been developed to simulate and study the evolution of ion charge states inside the trap region of an electron beam ion trap. In addition to atomic physics phenomena previously included in similar codes such as electron impact ionization, radiative recombination, and charge exchange, several aspects of the relevant physics such as dielectronic recombination, ionization heating, and ion cloud expansion have been included for the first time in the model. The code was developed using object oriented concepts with database support, making it readable, accurate, and well organized. The simulation results show a good agreement with various experiments, and give useful information for selection of operating conditions and experiment design.

Characterisation of virus transport and attenuation in epikarst using short pulse and prolonged injection multi-tracer testing

Attenuation processes controlling virus fate and transport in the vadose zone of karstified systems can strongly influence groundwater quality. This research compares the breakthrough of two bacteriophage tracers (H40/1 and T7), with contrasting properties, at subsurface monitoring points following application onto an overlying composite sequence of thin organic soil and weathered limestone (epikarst). Short pulse multi-tracer test results revealed that T7 (Source concentration, Co=1.8x106pfu/mL) and H40/1(Co=5.9x106pfu/mL) could reach sampling points 10m below ground less than 30 minutes after tracer application. Contrasting deposition rates, determined from simulated tracer responses, reflected the potential of the ground to differentially attenuate viruses. Prolonged application of both T7 (Co=2.3x104pfu/mL) and H40/1 (Co=1.3x105pfu/mL) over a five hour period during a subsequent test, in which ionic strength levels observed at monitoring points rose consistently, corresponded to a rapid rise in T7 levels, followed by a gradual decline before the end of tracer injection; this reflected reaction-limited deposition in the system. T7’s response contrasted with that of H40/1, whose concentration remained constant over a three hour period before declining dramatically prior to the end of tracer injection. Subsequent application of lower ionic strength tracer-free flush water generated a rapid rise in H40/1 levels and a more gradual release of T7. Results highlight the benefits of employing prolonged injection multi-tracer tests for identifying processes not apparent from conventional short pulse tests. Study findings demonstrate that despite rapid transport rates, the epikarst is capable of physicochemical filtration of viruses and their remobilization, depending on virus type and hydrochemical conditions.

MEASUREMENT AND CALCULATION OF ABSOLUTE SINGLE AND MULTIPLE CHARGE EXCHANGE CROSS SECTIONS FOR Feq+ IONS IMPACTING H2O

Charge exchange (CE) plays a fundamental role in the collisions of solar- and stellar-wind ions with lunar and planetary exospheres, comets, and circumstellar clouds. Reported herein are absolute cross sections for single, double, triple, and quadruple CE of Feq+ (q = 5-13) ions with H2O at a collision energy of 7q keV. One measured value of the pentuple CE is also given for Fe9+ ions. An electron cyclotron resonance ion source is used to provide currents of the highly charged Fe ions. Absolute data are derived from knowledge of the target gas pressure, target path length, and incident and charge-exchanged ion currents. Experimental cross sections are compared with new results of the n-electron classical trajectory Monte Carlo approximation. The radiative and non-radiative cascades following electron transfers are approximated using scaled hydrogenic transition probabilities and scaled Auger rates. Also given are estimates of cross sections for single capture, and multiple capture followed by autoionization, as derived from the extended overbarrier model. These estimates are based on new theoretical calculations of the vertical ionization potentials of H2O up to H2O10+.

Determination of absolute ion yields from a MALDI source through calibration of an image-charge detector

MALDI (matrix-assisted laser desorption/ionization) is one of the most important techniques used to produce large biomolecular ions in the gas phase. Surprisingly, the exact ionization mechanism is still not well understood and absolute values for the ion yields are scarce. This is in part due to the unknown efficiencies of typical detectors, especially for heavy biomolecular ions. As an alternative, charged particles can be non-destructively detected using an image-charge detector where the output voltage signal is proportional to the total charge within the device. In this paper, we report an absolute calibration which provides the voltage output per detected electronic charge in our experimental arrangement. A minimum of 3 x 10(3) ions were required to distinguish the signal above background noise in a single pass through the device, which could be further reduced using filtering techniques. The calibration results have been applied to raw MALDI spectra to measure absolute ion yields of both matrix and analyte ions.