Status of Flat Electron Beam Production

Last year at LINAC2000 [1] we reported our initial verification of the round beam (comparable transverse emittances) to flat beam (high transverse emittance ratio) transformation described by Brinkmann, Derbenev, and Flöttmann [2]. Further analysis of our data has confirmed that a transverse emittance ratio of approximately 50 was observed. Graphics representing observational detail are included here, and future plans outlined

A transcriptome-wide analysis deciphers distinct roles of G1 cyclins in temporal organization of the yeast cell cycle

Oscillating gene expression is crucial for correct timing and progression through cell cycle. In Saccharomyces cerevisiae, G1 cyclins Cln1-3 are essential drivers of the cell cycle and have an important role for temporal fine-tuning. We measured time-resolved transcriptome-wide gene expression for wild type and cyclin single and double knockouts over cell cycle with and without osmotic stress. Clustering of expression profiles, peak time detection of oscillating genes, integration with transcription factor network dynamics, and assignment to cell cycle phases allowed us to quantify the effect of genetic or stress perturbations on the duration of cell cycle phases. Cln1 and Cln2 showed functional differences, especially affecting later phases. Deletion of Cln3 led to a delay of START followed by normal progression through later phases. Our data and network analysis suggest mutual effects of cyclins with the transcriptional regulators SBF and MBF

Automated Ensemble Modeling with modelMaGe: Analyzing Feedback Mechanisms in the Sho1 Branch of the HOG Pathway

In systems biology uncertainty about biological processes translates into alternative mathematical model candidates. Here, the goal is to generate, fit and discriminate several candidate models that represent different hypotheses for feedback mechanisms responsible for downregulating the response of the Sho1 branch of the yeast high osmolarity glycerol (HOG) signaling pathway after initial stimulation. Implementing and testing these candidate models by hand is a tedious and error-prone task. Therefore, we automatically generated a set of candidate models of the Sho1 branch with the tool modelMaGe. These candidate models are automatically documented, can readily be simulated and fitted automatically to data. A ranking of the models with respect to parsimonious data representation is provided, enabling discrimination between candidate models and the biological hypotheses underlying them. We conclude that a previously published model fitted spurious effects in the data. Moreover, the discrimination analysis suggests that the reported data does not support the conclusion that a desensitization mechanism leads to the rapid attenuation of Hog1 signaling in the Sho1 branch of the HOG pathway. The data rather supports a model where an integrator feedback shuts down the pathway. This conclusion is also supported by dedicated experiments that can exclusively be predicted by those models including an integrator feedback

First Observation of Self-Amplified Spontaneous Emission in a Free-Electron Laser at 109 nm Wavelength

We present the first observation of Self-Amplified Spontaneous Emission (SASE) in a free-electron laser (FEL) in the Vacuum Ultraviolet regime at 109 nm wavelength (11 eV). The observed free-electron laser gain (approx. 3000) and the radiation characteristics, such as dependency on bunch charge, angular distribution, spectral width and intensity fluctuations all corroborate the existing models for SASE FELs.Comment: 6 pages including 6 figures; e-mail: [email protected]

Molecular Insights into Reprogramming-Initiation Events Mediated by the OSKM Gene Regulatory Network

Somatic cells can be reprogrammed to induced pluripotent stem cells by over-expression of OCT4, SOX2, KLF4 and c-MYC (OSKM). With the aim of unveiling the early mechanisms underlying the induction of pluripotency, we have analyzed transcriptional profiles at 24, 48 and 72 hours post-transduction of OSKM into human foreskin fibroblasts. Experiments confirmed that upon viral transduction, the immediate response is innate immunity, which induces free radical generation, oxidative DNA damage, p53 activation, senescence, and apoptosis, ultimately leading to a reduction in the reprogramming efficiency. Conversely, nucleofection of OSKM plasmids does not elicit the same cellular stress, suggesting viral response as an early reprogramming roadblock. Additional initiation events include the activation of surface markers associated with pluripotency and the suppression of epithelial-to-mesenchymal transition. Furthermore, reconstruction of an OSKM interaction network highlights intermediate path nodes as candidates for improvement intervention. Overall, the results suggest three strategies to improve reprogramming efficiency employing: 1) anti-inflammatory modulation of innate immune response, 2) pre-selection of cells expressing pluripotency-associated surface antigens, 3) activation of specific interaction paths that amplify the pluripotency signal

Secondary electron emission in a photocathode rf gun

During the last decades, photocathode rf guns have been proven to be successful for providing very high quality electron beams required for vacuum ultraviolet and x-ray free-electron lasers. Beam dynamics simulations show that the electron beam quality in a rf gun depends strongly on the beam dynamics in the vicinity of the cathode. Therefore, the injection process plays a significant role in the beam performance. Several codes are available to simulate the beam dynamics in the gun. They are able to track the beam under the influence of external fields and space charge forces, but details of the emission processes are still missing in these simulations. In photocathode rf guns, the electron beams have a high charge density. Especially during emission from the cathode, the electrons have a very low velocity and experience high longitudinal space charge forces counteracting the applied accelerating field. Because of the space charge field, some part of the electrons emitted from the cathode might move backward to the cathode where they can produce secondary electrons. A high electric field in the gun cavity, on the other hand, generates a large amount of dark current. If the field-emitted electrons from the cathode or any other surface inside the cavity hit the cathode, secondary electrons can be produced as well. For a detailed understanding of the electron beam and dark current in a rf gun, simulations including a model of the secondary electron emission are necessary. In this paper, a simple model is discussed with an application to the beam dynamics at high emission phases in rf guns. Detailed simulations have been done in comparison to measurements at the Photo Injector Test Facility at DESY in Zeuthen. The primary electrons which are photoemitted from the cathode and the secondary electrons which are produced by the primaries at the cathode could be clearly distinguished in measurements and simulations

Secondary electron emission in a photocathode rf gun

During the last decades, photocathode rf guns have been proven to be successful for providing very high quality electron beams required for vacuum ultraviolet and x-ray free-electron lasers. Beam dynamics simulations show that the electron beam quality in a rf gun depends strongly on the beam dynamics in the vicinity of the cathode. Therefore, the injection process plays a significant role in the beam performance. Several codes are available to simulate the beam dynamics in the gun. They are able to track the beam under the influence of external fields and space charge forces, but details of the emission processes are still missing in these simulations. In photocathode rf guns, the electron beams have a high charge density. Especially during emission from the cathode, the electrons have a very low velocity and experience high longitudinal space charge forces counteracting the applied accelerating field. Because of the space charge field, some part of the electrons emitted from the cathode might move backward to the cathode where they can produce secondary electrons. A high electric field in the gun cavity, on the other hand, generates a large amount of dark current. If the field-emitted electrons from the cathode or any other surface inside the cavity hit the cathode, secondary electrons can be produced as well. For a detailed understanding of the electron beam and dark current in a rf gun, simulations including a model of the secondary electron emission are necessary. In this paper, a simple model is discussed with an application to the beam dynamics at high emission phases in rf guns. Detailed simulations have been done in comparison to measurements at the Photo Injector Test Facility at DESY in Zeuthen. The primary electrons which are photoemitted from the cathode and the secondary electrons which are produced by the primaries at the cathode could be clearly distinguished in measurements and simulations

Design and characterization of permanent magnetic solenoids for REGAE

REGAE is a small electron linear accelerator at DESY. In order to focus short and low charged electron bunches down to a few μm permanent magnetic solenoids were designed, assembled and field measurements were done. Due to a shortage of space close to the operation area an in-vacuum solution has been chosen. Furthermore a two-ring design made of wedges has been preferred in terms of beam dynamic issues. To keep the field quality of a piecewise built magnet still high a sorting algorithm for the wedge arrangement including a simple magnetic field model has been developed and used for the construction of the magnets. The magnetic field of these solenoids has been measured with high precision and compared to simulations