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  • 1
    Electronic Resource
    Electronic Resource
    Type 1 fimbriae and extracellular polysaccharides are preeminent uropathogenic Escherichia coli virulence determinants in the murine urinary tract (2002)
    Oxford, UK : Blackwell Science Ltd.
    Molecular microbiology 45 (2002), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Escherichia coli is the leading cause of urinary tract infections (UTIs). Despite the association of numerous bacterial factors with uropathogenic E. coli (UPEC), few such factors have been proved to be required for UTI in animal models. Previous investigations of urovirulence factors have relied on prior identification of phenotypic characteristics. We used signature-tagged mutagenesis (STM) in an unbiased effort to identify genes that are essential for UPEC survival within the murine urinary tract. A library of 2049 transposon mutants of the prototypic UPEC strain CFT073 was constructed using mini-Tn5 km2 carrying 92 unique tags and screened in a murine model of ascending UTI. After initial screening followed by confirmation in co-infection experiments, 19 survival-defective mutants were identified. These mutants were recovered in numbers 10 1 - to 10 6 -fold less than the wild type in the bladder, kidneys or urine or at more than one site. The transposon junctions from each attenuated mutant were sequenced and analysed. Mutations were found in: (i) the type 1 fimbrial operon; (ii) genes involved in the biosyn-thesis of extracellular polysaccharides including group I capsule, group II capsule and enterobacterial common antigen; (iii) genes involved in metabolic pathways; and (iv) genes with unknown function. Five of the genes identified are absent from the genome of the E. coli K-12 strain. Mutations in type 1 fimbrial genes resulted in severely attenuated colonization, even in the case of a mutant with an insertion upstream of the fim operon that affected the rate of fimbrial switching from the ‘off’ to the ‘on’ phase. Three mutants had insertions in a new type II capsule biosynthesis locus on a pathogenicity island and were impaired in the production of capsule in vivo . An additional mutant with an insertion in wecE was unable to synthesize enterobacterial common antigen. These results confirm the pre-eminence of type 1 fimbriae, establish the importance of extracellular polysaccharides in the pathogenesis of UTI and identify new urovirulence determinants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2002.03078.x
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of the dominant glandless gene Gl2e on agronomic and fibre characters of Upland cotton (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 119 (2000), S. 0 
    Details
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Seven pairs of near-isogenic lines (glandless vs. glanded) and the recurrent parents were used to determine the effects of the dominant glandless gene from ‘Hai 1’(Gossypium barbadense) on agronomic, fibre, and seed characters in Upland cotton, Gossypium hirsutum, backgrounds. The results showed that there were no apparent linkage associations of the glandless gene on most agronomic, fibre and seed characters of Upland cotton, except for seed quality. The glandless line derived from ‘Liaomian 7’had significantly more protein (489.6 g/kg), and that from H237 had significantly more oil (362.4 g/kg) and had the largest oil index (2.70 g) and protein index (3.03 g). The gossypol content of seed in dominant glandless lines in Upland cotton was very low (〈0.04 g/kg). Therefore, it is suggested that the glandless gene can play an important role in breeding glandless or low seed-gossypol Upland cotton cultivars.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1439-0523.2000.00446.x
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  • 3
    Electronic Resource
    Electronic Resource
    Cavity eigenmodes for a free-electron laser (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 1669-1675 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The cavity transfer matrix for the round trip of a light pulse in the optical resonator of the National Institute of Standards and Technology/Naval Research Laboratory free-electron laser oscillator is derived. The cavity eigenmodes and the corresponding eigenvalues are obtained, using an expansion in Gaussian–Laguerre vacuum modes, by numerical diagonalization. The fractional power loss per eigenmode, caused by the finite sizes of the cavity mirrors and apertures, is determined. It is found that the losses are very small over the entire wavelength regime of operation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345634
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  • 4
    Electronic Resource
    Electronic Resource
    Chaotic electron motion caused by sidebands in free electron lasers (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 3387-3402 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron dynamics in a free electron laser (FEL) is studied in the case when the radiation field contains many modes. This situation arises when unstable modes (sidebands) are excited during operation. It is observed that when the strength of these sidebands exceeds certain levels the electron motion becomes chaotic. This may lead to extensive particle detrapping and loss of amplification for the FEL signal. The threshold for the onset of stochastic electron motion is computed. The evolution of the trapped electron distribution exhibits a diffusive behavior. The rate of particle detrapping is parametrized by the diffusion coefficient @FD in action space. The e-folding length for the number of trapped electrons is parametrized by J2s/@FD, where Js is the action at the separatrix. It is found that the diffusion rates are related to the type of the sideband spectrum. The diffusion coefficient is always proportional to the ratio of the sideband power in all frequencies to the power of the carrier signal. The coefficient of the proportionality, however, scales differently on the FEL parameters for each of the three spectral categories: a narrow, a broad discrete, and a broad continuous spectrum. The diffusion coefficient is computed analytically for the last two cases and is in good agreement with numerical results. The narrow spectrum yields the highest and the broad continuous the lowest diffusion rates under constant sideband power. It is also found that, in all cases, the diffusion length, measured in wiggler periods, is independent of the electron energy γ.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866904
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  • 5
    Electronic Resource
    Electronic Resource
    Higher harmonic generation in the induced resonance electron cyclotron maser (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 924-929 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Operation of the induced resonance electron cyclotron (IREC) maser [Appl. Phys. Lett. 49, 1154 (1986); Nucl. Instrum. Methods Phys. A 250, 36 (1986)] at Doppler upshifted cyclotron harmonics is studied. A set of fast-time averaged nonlinear equations of motion is derived for the particle motion near an arbitrary harmonic at any index of refraction. The small signal efficiency is computed analytically and the minimum current to start the cavity oscillations is obtained. The nonlinear equations of motion are integrated numerically. The interaction efficiency at the first few harmonics is found to be comparable to the efficiency at the fundamental. The sensitivity of the efficiency to beam thermal spreads is minimized by proper selection of the index of refraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866776
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  • 6
    Electronic Resource
    Electronic Resource
    Betatron-synchrotron detrapping in a tapered wiggler free-electron laser (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 2019-2021 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Betatron-synchrotron resonance detrapping is shown to take place when the wiggler magnetic field amplitude is tapered. This resonance exists even if the radiation wave fronts are not curved and is dependent on the transverse gradient of the tapered wiggler field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865381
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical consequences of wiggler field error reduction techniques on free-electron laser performance (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 781-796 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: There have been extensive studies on the effects of intrinsic field errors on the operation and performance of free-electron lasers (FEL's) based predominantly on simple models for the spatial form and statistical properties of the field errors. In some cases, the effects of compensation magnets or steering coils have been included as a method of reducing the deleterious effects of field errors. In the present study the effects of (i) compensation magnets, (ii) general spatial forms that are more realistic models of experimental wigglers, and (iii) statistical correlations of the field errors are considered. This theoretical study has resulted in a quantitative means of measuring the relative merit of these experimental techniques for reducing wiggler field error effects. These means of comparative analysis yield important criteria for experimental design and modeling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859874
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  • 8
    Electronic Resource
    Electronic Resource
    Stability regimes in a helical quadrupole focusing accelerator−theory and simulation (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 204-211 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The inclusion of helical quadrupole (stellarator) and axial guide fields in high current spiral line or recirculating accelerator configurations provides a high tolerance to energy mismatch and confines the beam against space charge forces. Such a configuration is studied via three-dimensional particle simulation. It is found that the electron beam centroid motion can interact with the external fields and with the TE11 waveguide mode to obtain (i) highly unstable particle orbits, (ii) the electromagnetic three-wave instability, or (iii) a fully stable beam. Theoretical stability conditions are presented in the limit of zero beam current and are found to be good predictors of simulation results. Minor departures from the stability conditions at high current are discussed in terms of the full linear dispersion relation. Saturation of the instability without beam loss is observed in some cases. This is the result of detuning in the relativistic cyclotron wave number as the beam energy and axial velocity decrease. The effectiveness of this detuning mechanism is evaluated for the various regimes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859938
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  • 9
    Electronic Resource
    Electronic Resource
    Dynamics of space-charge waves in the laser beat wave accelerator (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 1974-1983 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The excitation of plasma waves by two laser beams, whose frequency difference is approximately the plasma frequency, is analyzed. Our nonlinear analysis is fully relativistic in the axial and transverse directions and includes mismatching of the laser beat frequency to the plasma frequency, time dependent laser amplitudes, and an applied transverse magnetic field (surfatron configuration). Our analytical results for the large amplitude plasma waves include an axial constant of motion, accelerating electric field, and its phase velocity. The analytical results in the weak laser power limit are in good agreement with numerical results obtained from the complete equations. The imposed transverse magnetic field is found to increase the effective plasma frequency, but has little effect on the plasma dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865375
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  • 10
    Electronic Resource
    Electronic Resource
    The structure of the sideband spectrum in free electron lasers (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 1708-1719 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The one-dimensional, fast time averaged Hamiltonian is derived in a free electron laser (FEL) for electrons passing through a constant parameter wiggler and a radiation field. The exact unperturbed orbits without sidebands are obtained for all particles and arbitrary strength of the main signal. Integration, in action-angle variables, of the linearized kinetic equation with perturbing sidebands over the unperturbed orbits yields the sideband growth rate including both trapped and untrapped particles. The structure and scaling of the unstable spectrum are different from previous results obtained for electrons localized at the bottom of the ponderomotive well. It is found that upper and lower sidebands that are symmetric relative to the FEL frequency have opposite growth rates. There is no differentiation in the magnitude of the gain between upper and lower sidebands. The stability is determined by the sign of df0/dωb, the relative population of quantized oscillators with energy quantum (h-dash-bar)ωb, where ωb is the synchrotron frequency in resonance with the sideband. The shear dωb/dJ, where J is the action variable, is stabilizing and distributions with gradients df0/dJ localized near the separatrix have the minimum growth rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866709
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