D. Smith

Keele University, Newcastle-under-Lyme, England, United Kingdom

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Publications (235)414.64 Total impact

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    ABSTRACT: To characterize the volatile metabolites produced by genotypically diverse strains of Pseudomonas aeruginosa in order to evaluate their potential for use as biomarkers of lung infection in noninvasive breath analysis. Volatile organic compounds (VOCs) emitted from 36 clinical strains of Ps. aeruginosa (belonging to different multilocus sequence types) cultured in liquid and on solid media were analysed by gas chromatography mass spectrometry (GC-MS) and selected ion flow tube mass spectrometry (SIFT-MS). Several previously identified VOCs were detected, including ethanol, acetone, 2-butanone, 2-pentanone, isoprene, aminoacetophenone, dimethyl sulphide, dimethyl disulphide, dimethyl trisulphide and methyl thiocyanate. Additionally, significant production of 3-methyl-butanone, acetophenone, methylthioacetate and methyl thiobutanoate was observed for the first time in this study. SIFT-MS quantifications of VOCs showed high variability between genotypically distinct strains. The data obtained indicate that the production rates of the volatile biomarkers of Ps. aeruginosa vary by two orders of magnitude between different strains cultured under the same conditions. Similar variability was observed for both liquid and solid media. Inter-strain genotypic variability strongly influences the concentrations of the volatile biomarkers from Ps. aeruginosa. A group of several biomarkers quantified in real time in exhaled breath may thus provide a more valuable indicator of the course of pulmonary infections compared to a single biomarker.
    Journal of Applied Microbiology 06/2012; 113(3):701-13. · 2.39 Impact Factor
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    ABSTRACT: There is increasing interest in using the cyanogenic properties of Pseudomonas aeruginosa to develop a nonmicrobiological method for its detection. Prior to this, the variation in cyanide production between different P. aeruginosa strains needs to be investigated. Hydrogen cyanide (HCN) released into the gas phase by 96 genotyped P. aeruginosa samples was measured using selected ion flow tube-mass spectrometry after 24, 48, 72 and 96 h of incubation. The HCN produced by a range of non-P. aeruginosa cultures and incubated blank plates was also measured. All P. aeruginosa strains produced more HCN than the control samples, which generated extremely low levels. Analysis across all time-points demonstrated that nonmucoid samples produced more HCN than the mucoid samples (p=0.003), but this relationship varied according to strain. There were clear differences in the headspace HCN concentration for different strains. Multivariate analysis of headspace HCN for the commonest strains (Liverpool, Midlands_1 and Stoke-on-Trent, UK) revealed a significant effect of strain (p<0.001) and a borderline interaction of strain and phenotype (p=0.051). This evidence confirms that all P. aeruginosa strains produce HCN but to varying degrees and generates interest in the possible future clinical applications of the cyanogenic properties of P. aeruginosa.
    European Respiratory Journal 04/2011; 38(2):409-14. · 7.13 Impact Factor
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    ABSTRACT: In selected ion flow tube mass spectrometry, SIFT-MS, analyses of humid air and breath, it is essential to consider and account for the influence of water vapour in the media, which can be profound for the analysis of some compounds, including H(2)CO, H(2)S and notably CO(2). To date, the analysis of methane has not been considered, since it is known to be unreactive with H(3)O(+) and NO(+), the most important precursor ions for SIFT-MS analyses, and it reacts only slowly with the other available precursor ion, O(2) (+). However, we have now experimentally investigated methane analysis and report that it can be quantified in both air and exhaled breath by exploiting the slow O(2) (+)/CH(4) reaction that produces CH(3)O(2) (+) ions. We show that the ion chemistry is significantly influenced by the presence of water vapour in the sample, which must be quantified if accurate analyses are to be performed. Thus, we have carried out a study of the loss rate of the CH(3)O(2) (+) analytical ion as a function of sample humidity and deduced an appropriate kinetics library entry that provides an accurate analysis of methane in air and breath by SIFT-MS. However, the associated limit of detection is rather high, at 0.2 parts-per-million, ppm. We then measured the methane levels, together with acetone levels, in the exhaled breath of 75 volunteers, all within a period of 3 h, which shows the remarkable sample throughput rate possible with SIFT-MS. The mean methane level in ambient air is seen to be 2 ppm with little spread and that in exhaled breath is 6 ppm, ranging from near-ambient levels to 30 ppm, with no significant variation with age and gender. Methane can now be included in the wide ranging analyses of exhaled breath that are currently being carried out using SIFT-MS.
    Rapid Communications in Mass Spectrometry 05/2010; 24(9):1296-304. · 2.51 Impact Factor
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    ABSTRACT: Using selected ion flow tube mass spectrometry (SIFT-MS), measurements have been made of the levels of several metabolites in the exhaled breath of 200 healthy school children. Thus, concentration distributions of each metabolite have been obtained for the first time in the paediatric age range. The median values (in parentheses) of the concentrations in parts per billion, ppb, were ammonia (628), acetone (297), methanol (193), ethanol (187), isoprene (37), propanol (16), acetaldehyde (23) and pentanol (15). Hydrogen cyanide was not present in the breath above the detection limit of 2 ppb in the majority of subjects. The water vapour level (humidity) of the breath samples was routinely measured as a check on the sample integrity. Such data are essential if SIFT-MS breath analyses are to be used as a clinical tool to aid diagnosis and/or as a monitor of disease in children. The levels of metabolites usually followed a log-normal distribution and the levels of some compounds were similar to those obtained previously in adults. Lower values were found in the levels of acetone, ammonia, methanol and isoprene. There were no major variations in relation to gender. Some metabolites showed significant variation in relation to age and body mass index. To our knowledge, these are the first measurements of exhaled mouth breath pentanol levels. The median ammonia levels in mouth-exhaled breath of these children decreased with age, whereas in older adults, ammonia has been shown to increase with age. Breath acetone levels were significantly increased for those who had not eaten for more than 6 h prior to providing the breath sample, although dietary control was not a mandatory aspect of the protocol.
    Journal of Breath Research 09/2009; 3(3):036001. · 2.57 Impact Factor
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    ABSTRACT: Selected ion flow tube mass spectrometry, SIFT-MS. has been used to investigate if absolute levels of trace compounds in the headspace of ethanol/water vapour mixture can be quantified. This case study was directed towards the analysis of methylamine in distilled ethanol of agricultural origin because of its relevance to quality control legislation in the distillery industry. This has required a detailed study of the ion chemistry occurring - initiated by H(3)O(+) precursor ions - when ethanol/water vapour mixtures are introduced into the H(3)O(+)/helium carrier gas swarm and has resulted in the construction of a full scheme of the complex ionic reactions that occur. It has been found that under the SIFT-MS flow reactor conditions (He pressure 130 Pa and temperature 299 K) the terminating ions of the several parallel and sequential reactions that occur are the proton bound ethanol clusters ions. C(2)H(5)OH(2)(+)(C(2)H(5)OH)(n). with n = 1,2,3, proton bound trimer (n = 2) being the dominant species. These ethanol cluster ions can be used as precursor (reagent) ions for the chemical ionisation of the methylamine present in the ethanol/water vapour, which produces two characteristic product ions CH(3)NH(2)H(+)(C(2)H(5)OH)(1,2) that are used for the methylamine analysis. The ratio of the product ion count rate to the precursor ion count rate is used in an analogous way to the routinely used for SIFT-MS analyses to quantify the methylamine concentration. The results of calibration experiments show that using SIFT-MS it is possible to quantify methylamine in liquid ethanol/water mixtures at levels of 0.1 mg/L or greater. (C) 2009 Elsevier B.V. All rights reserved.
    International Journal of Mass Spectrometry 09/2009; 286(1):1-6. · 2.23 Impact Factor
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    ABSTRACT: We have carried out a selected ion flow tube mass spectrometry (SIFT-MS) study of the concentrations of the sulfur-containing compounds H(2)S (using H(3)O(+) precursor ions), CH(3)SH (H(3)O(+)), (CH(3))(2)S (O(2)(+)), (CH(3))(2)S(2) (NO(+)) and CS(2) (O(2)(+)) in single exhalations of mouth-exhaled breath and nose-exhaled breath and in the static gas in the oral cavity for two healthy volunteers. The primary purpose of the study was to show how compounds present in breath at levels as low as a part per billion (ppb) can be identified and quantified if the overlap of 'impurity' isobaric ions with the analytical product ions for each trace compound is identified and accounted for. The H(2)S measurements are straightforward using H(3)O(+) precursor ions, since no overlapping ions are recognized and its breath concentration is relatively high at typically 20-70 ppb. Thus, its concentration distribution for two healthy volunteers has been obtained over a period of a few weeks. The situation is very similar for CH(3)SH, but to analyse this compound we had to study the kinetics of its reactions with the SIFT-MS reagent ions H(3)O(+), NO(+) and O(2)(+) in order to provide the required kinetics library data for this compound. It is seen that CH(3)SH, (CH(3))(2)S and (CH(3))(2)S(2) are present in the mouth breath/cavity at lower levels of <10 ppb. The measurements of the levels of H(2)S and these compounds in the nose-exhaled breath and the closed mouth indicate that they are largely produced in the oral cavity, although there is some indication that (CH(3))(2)S is partially systemic in these two volunteers. It was not possible to quantify CS(2) in the breath because of serious interference (overlapping ions) due to the presence of carbon dioxide and acetone that inevitably occur in exhaled breath. This study paves the way for the accurate analysis of these sulfur compounds in halitosis and potentially for probing the diseased state, especially liver disease, by breath analysis. To demonstrate the simplicity of measuring these compounds when they are present at levels of about 100 ppb and greater, data are presented on the emissions of these sulfur-containing compounds from Pseudomonas bacterial cultures in vitro.
    Journal of Breath Research 12/2008; 2(4):046004. · 3.59 Impact Factor
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    P Spanĕl, D Smith
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    ABSTRACT: Selected ion flow tube mass spectrometry, (SIFT-MS), is a technique for simultaneous real-time quantification of several trace gases in air and exhaled breath. It relies on chemical ionization of the trace gas molecules in air/breath samples introduced into helium carrier gas, using H(3)O(+), NO(+) and O(2)(+) reagent (precursor ions). Reactions between the precursor ions and the trace gas molecules proceed for an accurately defined time, the precursor and product ions being detected and counted by a downstream mass spectrometer. Absolute concentrations of trace gases in single breath exhalation can be determined by SIFT-MS down to parts-per-billion (ppb) levels, obviating sample collection into bags or onto traps. Calibration using chemical standards is not required, as the concentrations are calculated using the known reaction rate constants and measured flow rates and pressures. SIFT-MS has been used for many pilot investigations in several areas of research, especially as a non-invasive breath analysis tool to investigate physiological processes in humans and animals, for clinical diagnosis and for therapeutic monitoring. Examples of the results obtained from several such studies are outlined to demonstrate the potential of SIFT-MS for trace gas analysis of air, exhaled breath and the headspace above liquids.
    European Journal of Mass Spectrometry 02/2007; 13(1):77-82. · 1.17 Impact Factor
  • D Smith, P Spanel
    Breath Analysis: for Clinical Diagnosis and ATherapeutic Monitoring; 01/2005
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    ABSTRACT: A simple ion source is described that consists of a glass discharge tube positioned judiciously in a rectangular waveguide resonator that is directly coupled to an under-run standard magnetron. This ion source operates well with gas mixtures, including rare gases, air and water vapour in the pressure range 10-100 Pa and at magnetron powers within the range 15-40 W. The main advantage of this magnetron/cavity arrangement is the absence of mechanically adjustable parts (aerial and tuning stub), in contrast to other commonly used arrangements that combine a cavity resonator that is connected to the magnetron via a launcher and a coaxial cable.
    Plasma Sources Science and Technology 05/2004; 13(2):282-284. · 3.06 Impact Factor
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    ABSTRACT: We have carried out a selected ion flow tube, SIFT, study of the reactions of H
    International Journal of Mass Spectrometry 08/2003; 228(2-3):269-283. · 2.23 Impact Factor
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    D Trunec, P Spanel, D Smith
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    ABSTRACT: The electron energy distribution functions for electron thermalization in helium and argon afterglow plasmas have been calculated taking into account electron-neutral and electron-electron collisions. This work shows that electron-electron collisions can lead to the Maxwellization of the electron energy distribution function and thus to different rates of electron thermalization. (C) 2003 Elsevier Science B.V. All rights reserved.
    Chemical Physics Letters 05/2003; 372(5-6):728-732. · 1.99 Impact Factor
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    ABSTRACT: The results about selected ion flow tube/mass spectrometry (SIFT/MS) study of the different compounds in petrol and diesel vapor's using H3O+, NO+ as the precursor ions are reported. We assume both petrol and diesel are made up of CHs, including alkanes (CnH2n+2), alkenes or cyclokanes (CnH2n) alkynes or dienes (CnH2n-2) and aromatic hydrocarbons (CnH2n-6). Among these compounds, the alkanes are the predominant species both in diesel and petrol vapors; The most obvious difference between petrol and diesel vapor is. the presence of a greater abundance of long chain aliphatic CHs in the diesel vapor. In this paper, the mass spectra of petrol vapor using the precursors of the H3O+ NO+ and the quantitative analysis results of, the compounds in the petrol and diesel vapors are also presented.
  • C V Goodall, D Smith
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    ABSTRACT: A diversity of opinion exists at the present time concerning the interpretation of single Langmuir probe characteristics, in particular with respect to the location of space potential and the determination of charged particle number densities from the characteristics. This work describes measurements made with very small Langmuir probes in gaseous afterglow plasmas at room temperature where conditions for a study of this kind are expected to offer particular advantages. A comparison is made of the values of electron densities obtained from the characteristics using six methods which are commonly used. Good agreement is found to exist between those deduced from the orbital limited characteristics in the accelerating region for electrons and those calculated from the probe current at the inflexion point of the characteristics. That these are also in tolerable agreement with those obtained using the intersecting tangents method is thought to be fortuitous.
    Plasma Physics 12/2002; 10(3):249.
  • P Spanel, TS Wang, D Smith
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    ABSTRACT: A selected ion flow tube study has been carried out of the reactions of H3O+, NO+ and O-2(+) with 1,2-ethanediol (ethylene glycol), 1,2- and 1,3-propanediol, 1,2-, 1,3- and 1,4-butanediol, 1,5-pentanediol, 1,2-cyclopentanediol and 2-thioethanol (or 2-mercapto-ethanol, HOCH2CH2SH). The reactions of these species with H3O+ ions are assumed to proceed via exothermic proton transfer, their rate coefficients, k(c) being equal to the calculated collisional rate coefficients, k(c). On this basis, the experimental k values for most of the NO+ and O-2(+) reactions are also close to their respective k(c) values, although the k values for three of the NO+ reactions are measurably smaller than their k(c) values. In the H3O+ reactions the protonated parent ions , MH+, are always minor product ions. (MH-H2O)(+), resulting from the loss of H2O from the nascent MH+ ions being the major product ions. Three-body rate coefficients are derived for the association reactions of these product ions with water molecules. The most common process that occurs in the NO+ reactions is hydride ion transfer producing (M-H)(+) ions, but for the 1,4-butanediol and 1,5-pentanediol reactions, hydride ion transfer and parallel H2O elimination occur. The O-2(+) reactions all lead to multiple product ions, which must result from very diverse fragmentation processes. The value to selected ion flow tube mass spectrometry of these kinetic data is briefly alluded to. (Int J Mass Spectrom 218 (2002) 227-236) (C) 2002 Elsevier Science B.V. All rights reserved.
    International Journal of Mass Spectrometry 07/2002; 218(3):227-236. · 2.23 Impact Factor
  • D Smith, A G Dean, N G Adams
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    ABSTRACT: Measurements are described of the temporal and spatial variations of the space charge fields in afterglow plasmas together with parallel measurements of electron density (ne), positive ion density (n+), negative ion density (n-), electron temperature (Te) and mass-analysed wall currents of both positive and negative ions. In the case of the plasmas containing electrons and positive ions only, it has been shown that the spatial variation of plasma potential (Δ Va) is related to gradients in the charged particle densities and to the electron temperature via diffusion theory, and no complications in the sampling of positive ion wall currents with an orifice probe arise. For plasmas in which significant concentrations of negative ions exist, the previously observed `trapping' of negative ions within the plasma occurs, as manifest by a lack of negative ion wall current at early afterglow times followed later by a sudden onset. The probe measurements indicate a continuous diffusive loss of electrons and positive ions during the afterglow, whereas the negative ions remain within the plasma until ne has fallen to less, similar 10−2n- at which point an avalanche loss process of the remaining electrons begins which rapidly leads to the establishment of a negative-ion/positive-ion plasma. During the afterglow period, a progressive collapse of the wall potential and the ambipolar field occurs from those characteristic of an electron-dominated plasma to those of a negative-ion-dominated plasma. The sudden appearance of negative ion wall current is closely correlated with the avalanche collapse of the ambipolar field. The significance of these observations to mass-spectrometric sampling from afterglow plasma is discussed.
    Journal of Physics D Applied Physics 05/2002; 7(14):1944. · 2.52 Impact Factor
  • D Smith, I C Plumb
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    ABSTRACT: A detailed appraisal of the collisionless sheath single cylindrical Langmuir probe technique applied to the study of electron densities and temperatures in afterglow plasmas is described. It is shown that for positive probe potentials (V) no significant disturbance (`pseudodepletion') of the plasma occurs until the electron current to the probe (ie) approaches the natural diffusive positive ion current flowing to the reference electrodes. This is indicated by departures from linearity of ie2-V plots obtained in the orbital-limited current régime. Departures from linearity have also been observed due to probe sheath expansion resulting in departures from cylindrical geometry above a critical value of V. It is shown that, for values of V below those critical values signifying the onset of pseudodepletion and sheath expansion, meaningful probe characteristics can be obtained in afterglows from which accurate electron densities can be obtained. Also described are the effects which arise from temporal changes of electron temperature, and the resulting changes in floating potential Vf. The latter has been measured as a function of the electron temperature (obtained from plots of the electron retarding region) and is shown to substantiate the original Langmuir theoretical expression for Vf.
    Journal of Physics D Applied Physics 05/2002; 5(7):1226. · 2.52 Impact Factor
  • D Smith, M J Copsey
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    ABSTRACT: Mass spectrometric observations of helium afterglows by ion sampling from the walls of a large discharge vessel are described. It is shown that in very pure cataphoretically-cleaned helium in the pressure range 03 to 2 torr the only important processes occurring in the late afterglow are ambipolar diffusion of atomic and molecular ions and electrons, and conversion of atomic to molecular ions by three-body collisions with neutral helium atoms. The atomic and molecular ion mobilities corresponding to the observed diffusion rates are respectively 112 ± 04 cm2 v-1 s-1 and 159 ± 04 cm2 v-1 s-1, in acceptable agreement with several previous mobility measurements, and the value obtained for the three-body conversion coefficient, 85 ± 3 torr-2 s-1 (pressure reduced to 0 °C) is in good agreement with a recent similar measurement by other workers in a higher pressure range. The wall temperature of the discharge vessel during these measurements was 295 °K. Measurements carried out in helium samples which were not subjected to cataphoretic purification demonstrated the serious effect of small amounts of impurity on the decay rate of the molecular helium ion.
    Journal of Physics B Atomic and Molecular Physics 05/2002; 1(4):650.
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    ABSTRACT: Measurements are described of slow electron density decay rates in pure helium afterglow plasmas, using a very small single Langmuir probe, a technique not hitherto applied to the study of ambipolar diffusion. Values are obtained for the rate of conversion of He+ ions to He2+ ions and for the respective mobilities of these ions at a wall temperature of 295 °K, which are in reasonable agreement with values obtained by other workers using different techniques. This agreement is considered to indicate that depletion problems, which are expected to be most severe in slowly decaying plasmas, have been overcome by the utilization of very small probes. Evidence is also presented for the existence of elevated electron temperatures at times as late as 10 ms in the afterglow, and these results, together with those above, are critically discussed and compared in detail with the complementary mass spectrometric observations described in I.
    Journal of Physics B Atomic and Molecular Physics 05/2002; 1(4):660.
  • D Smith, I C Plumb
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    ABSTRACT: This paper describes the results obtained from a comparative study of the electron currents (ie) and positive-ion currents (i+) which flow to a small cylindrical Langmuir probe in pure rare-gas afterglow plasmas at low pressures. It is shown that within a predictable restricted range of charge density, linear plots of ie2 and i+2 against the probe-plasma potential difference could be obtained for positively and negatively biased probes respectively; which is in qualitative agreement with the Langmuir theory of orbital-limited-current collection. However, the values of the electron density (ne) and the apparent positive-ion density (n+) deduced from the slopes of the above plots were not equal; n+ always exceeding ne and related empirically to it via the mass of the positive ion m+ (in amu) thus: n+ = (1+007m+½)ne. It is suggested from additional experimental evidence that the values for ne are accurate and the discrepancy arises as a result of the inadequate theoretical description of the positive-ion currents flowing to the negatively biased probe. The data points of Tonks and Langmuir (1929) and of Shaeffer (1971) obtained in arc plasmas are shown to be consistent with the present results. The significance of these results to plasma diagnostics using probes is discussed.
    Journal of Physics D Applied Physics 05/2002; 6(2):196. · 2.52 Impact Factor
  • D Smith, N G Adams
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    ABSTRACT: This paper is concerned with an investigation of the plasma generated during the impact of hypervelocity microparticles with a metal target. A laboratory source of hypervelocity micron-sized iron particles is first described which utilizes a 2 MV Van de Graaff generator, followed by a discussion of the techniques used to determine the mass and velocity of the particles. On impact of the iron projectiles on a slatted molybdenum target, charge is generated, extracted from the region of impact by suitably biasing a gridded electrode, and subsequently detected using a conventional wideband electronic amplifier or an electron multiplier. It is shown statistically that during impact equal numbers of electrons and positive ions are produced - indicating plasma generation - and that the total charge released (Q) may be described empirically in terms of the mass (m) and velocity (v) of the particle by a simple power law relationship of the kind Qαmαvβ, with β = 32 ± 01 over the complete velocity range investigated (005 to 10 km s−1) and with α = 085 for v>1 km s−1 and 133 for v<1 km s−1. It is also shown that the charge extracted from the plasma reaches a maximum a few microseconds after impact and subsequently decays exponentially with a time constant of several micro-seconds. A crude mass analysis of the positive ions generated during the impact using a simple time-of-flight mass spectrometer has indicated that, over the velocity range investigated, the dominant ions in the spectrum are characteristic of the projectile and not the target material. From considerations of the relative abundance of the metal ions in the spectra, together with the known relative metal atom concentrations in the iron projectiles, the temperatures of the plasmas have been estimated (from Saha equilibrium considerations) to be of the order of several thousands of degrees Kelvin. In a detailed discussion, attempts are made to consider how the kinetic energy of the projectile is dissipated - eventually producing plasma - in terms of available theoretical models of hypervelocity impact. It is shown that the most satisfactory model of this very complex interaction appears to be one in which the relative importance of shock-wave propagation into the projectile and target materials is considered. Finally, a discussion of the properties and the temporal behaviour of the impact-produced plasma is presented in order to assess the relative importance of diffusion and recombination processes, thus to assist in the interpretation of the experimental results obtained in this study.
    Journal of Physics D Applied Physics 05/2002; 6(6):700. · 2.52 Impact Factor

Publication Stats

4k Citations
414.64 Total Impact Points


  • 1996–2010
    • Keele University
      • Institute for Science and Technology in Medicine
      Newcastle-under-Lyme, England, United Kingdom
  • 2000–2009
    • Academy of Sciences of the Czech Republic
      • J. Heyrovský Institute of Physical Chemistry
      Praha, Praha, Czech Republic
  • 1968–2002
    • University of Birmingham
      • School of Physics and Astronomy
      Birmingham, ENG, United Kingdom
  • 2001
    • University of Wales
      • Department of Physics
      Cardiff, Wales, United Kingdom
  • 1997
    • University Hospital Of North Staffordshire NHS Trust
      • Department of Renal Medicine
      Stoke-on-Trent, ENG, United Kingdom
  • 1993–1995
    • University of Innsbruck
      • Institute for Ion Physics and Applied Physics
      Innsbruck, Tyrol, Austria
  • 1992
    • University of Southampton
      Southampton, England, United Kingdom
  • 1984
    • Université Paris-Sud 11
      Orsay, Île-de-France, France
  • 1983–1984
    • Duke University
      • Department of Physics
      Durham, NC, United States