| 1. |
- Lumpkin, A. H., et al.
(författare)
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Evidence for microbunching "sidebands" in a saturated free-electron laser using coherent optical transition radiation
- 2002
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Ingår i: Physical Review Letters. - 1079-7114. ; 88:23, s. 4-4
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Tidskriftsartikel (refereegranskat)abstract
- We report the first measurements of z -dependent coherent optical transition radiation (COTR) due to electron-beam microbunching at high gains (>10(4) ) including saturation of a self-amplified spontaneous emission free-electron laser (FEL). In these experiments the fundamental wavelength was near 530 nm, and the COTR spectra exhibit the transition from simple spectra to complex spectra (5% spectral width) after saturation. The COTR intensity growth and angular distribution data are reported as well as the evidence for transverse spectral dependencies and an "effective" core of the beam being involved in microbunching.
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| 2. |
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| 3. |
- Biedron, Sandra G., et al.
(författare)
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Evolution of transverse modes in a high-gain free-electron laser
- 2004
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 528:1-2, s. 443-447
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Tidskriftsartikel (refereegranskat)abstract
- At the point of saturation in a high-gain free-electron laser (FEL) the light is fully transversely coherent. The number and evolution of the transverse modes is important for the effective tune-up and subsequent operation of FELs based on the photon beam characterization and in designing multi-module devices that rely on relatively stable saturation distances in each module. In the latter, this is particularly critical since each section will seed another module. Overall, in a single- or multi-module device, experimental users will desire stability in power and in photon beam quality. Using a numerical simulation code, the evolution of the transverse modes in the high-gain free-electron laser (FEL) is examined and is discussed. In addition, the transverse modes in the first few higher nonlinear harmonics are investigated.
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| 4. |
- Williams, P., et al.
(författare)
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Quorum sensing and the population-dependent control of virulence
- 2000
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 355:1397, s. 667-680
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Forskningsöversikt (refereegranskat)abstract
- One crucial feature of almost all bacterial infections is the need for the invading pathogen to reach a critical cell population density sufficient to overcome host defences and establish the infection. Controlling the expression of virulence determinants in concert with cell population density may therefore confer a significant survival advantage on the pathogen such that the host is overwhelmed before a defence response can be fully initiated. Many different bacterial pathogens are now known to regulate diverse physiological processes including virulence in a cell-density-dependent manner through cell-cell communication. This phenomenon, which relies on the interaction of a diffusible signal molecule (e.g. an N-acylhomoserine lactone) with a sensor or transcriptional activator to couple gene expression with cell population density, has become known as 'quorum sensing'. Although the size of the 'quorum' is likely to be highly variable and influenced by the diffusibility of the signal molecule within infected tissues, nevertheless quorum-sensing signal molecules can be detected in vivo in both experimental animal model and human infections. Furthermore, certain quorum-sensing molecules have been shown to possess pharmacological and immunomodulatory activity such that they may function as virulence determinants per se. As a consequence, quorum sensing constitutes a novel therapeutic target for the design of small molecular antagonists capable of attenuating virulence through the blockade of bacterial cell-cell communication.
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