208 research outputs found
Simulations of the Micro-Bunching Instability for SOLEIL and KARA Using Two Different VFP Solver Codes
The longitudinal dynamics of a bunched electron beam is an important aspect in the study of existing and the development of new electron storage rings. The dynamics depend on different beam parameters as well as on the interaction of the beam with its surroundings. A well established method for calculating the resulting dynamics is to numerically solve the Vlasov-Fokker-Planck equation. Depending on the chosen parameters and the considered wakefields and impedances, different effects can be studied. One common application is the investigation of the longitudinal micro-wave and micro-bunching instabilities. The latter occurs for short electron bunches due to self-interaction with their own emitted coherent synchrotron radiation (CSR). In this contribution, two different VFP solvers are used to simulate the longitudinal dynamics with a focus on the micro-bunching instability at the Soleil synchrotron and the KIT storage ring KARA (Karlsruhe Research Accelerator)
Synthesis of Polyhydroxylated Pyrano-Pyrrole Derivatives from Carbohydrate Precursors
The efficient synthesis of novel polyhydroxyâtetrahydropyranoâpyrroles from acetylenic carbohydrate precursors in three to four steps is described. The methodology involves, as key steps, the ring contraction of pyridazine intermediates obtained by an inverseâdemand DielsâAlder reaction and subsequent intramolecular lactonization
High repetition-rate electro-optic sampling: Recent studies using photonic time-stretch
Single-shot electro-optic sampling (EOS) is a powerful characterization tool for monitoring the shape of electron bunches, and coherent synchrotron radiation pulses. For reaching high acquisition rates, an efficient possibility consists to associate classic EOS systems with the so-called photonic time-stretch technique [1]. We present recent results obtained at SOLEIL and ANKA using this strategy. In particular, we show how a high sensitivity variant of photonic time stretch [2] EOS enabled to monitor the CSR pulses emitted by short electron bunches at SOLEIL [3]. We could thus confirm in a very direct way the theories predicting an interplay between two physical processes. Below a critical bunch charge, we observe a train of identical THz pulses stemming from the shortness of the electron bunches. Above this threshold, CSR emission is dominated by drifting structures appearing through spontaneous self-organization. We also consider the association of time-stretch and EOS for recording electron bunch near fields at high repetition rate. We present preliminary results obtained at ANKA, aiming at recording the electron bunch shape evolution during the microbunching instability
Expression of the SmBâČ splicing protein in rodent cells capable of following an alternative RNA splicing pathway
AbstractThe expression of the SmB and SmBâČ spliceosome proteins in a variety of cell types and tissues has been investigated. Although SmB is found in all cells studied, the SmBâČ protein is found only in a small number of rodent cell types. The presence of this protein is correlated with the ability to utilize an alternative pathway of RNA splicing which is not available in most cell types. This is the first demonstration of tissue specific expression of a protein component of the spliceosome and suggests a role for SmBâČ in the regulation of some cases of alternative RNA splicing
TRH: Pathophysiologic and clinical implications
Thyrotropin releasing hormone is thought to be a tonic stimulator of the pituitary TSH secretion regulating the setpoint of the thyrotrophs to the suppressive effect of thyroid hormones. The peptide stimulates the release of normal and elevated prolactin. ACTH and GH may increase in response to exogenous TRH in pituitary ACTH and GH hypersecretion syndromes and in some extrapituitary diseases.
The pathophysiological implications of extrahypothalamic TRH in humans are essentially unknown.
The TSH response to TRH is nowadays widely used as a diganostic amplifier in thyroid diseases being suppressed in borderline and overt hyperthyroid states and increased in primary thyroid failure. In hypothyroid states of hypothalamic origin, TSH increases in response to exogenous TRH often with a delayed and/or exaggerated time course.
But in patients with pituitary tumors and suprasellar extension TSH may also respond to TRH despite secondary hypothyroidism. This TSH increase may indicate a suprasellar cause for the secondary hypothyroidism, probably due to portal vessel occlusion. The TSH released in these cases is shown to be biologically inactive
LUNEX5 : A FEL PROJECT TOWARDS THE FIFTH GENERATION IN FRANCE
ISBN978-3-95450-117-5 - http://accelconf.web.cern.ch/AccelConf/FEL2011/papers/tupa09.pdfInternational audienc
DĂ©mences : oĂč sont les corps de Lewy ?
La dĂ©mence Ă corps de Lewy (DCL) est la deuxiĂšme cause de dĂ©mence dĂ©gĂ©nĂ©rative du sujet ĂągĂ©, dans les grandes sĂ©ries autopsiques. Dans la rĂ©alitĂ© quotidienne des centres mĂ©moire pourtant, la DCL reprĂ©sente une faible proportion des diagnostics cliniques, avec une forte disparitĂ© entre les centres. Plusieurs raisons peuvent rendre compte de la faible sensibilitĂ© du diagnostic de DCL : lâimprĂ©cision et la subjectivitĂ© des critĂšres diagnostiques existants ; la place insuffisante donnĂ©e Ă certains signes non-moteurs (troubles du comportement en sommeil paradoxal, dysautonomie) ; enfin et surtout lâassociation quasi constante de la pathologie de Lewy Ă une pathologie de type Alzheimer, qui domine rapidement le phĂ©notype clinique. Ă lâheure de lâessor des thĂ©rapies ciblĂ©es contre les agrĂ©gats protĂ©iques, de nouvelles Ă©chelles cliniques permettant dâapprĂ©hender la coexistence de la pathologie de Lewy dans la maladie dâAlzheimer sont plus que jamais nĂ©cessaires
A NEW SCHEME FOR ELECTRO-OPTIC SAMPLING AT RECORD REPETITION RATES: PRINCIPLE AND APPLICATION TO THE FIRST (TURN-BY-TURN) RECORDINGS OF THz CSR BURSTS AT SOLEIL
Abstract The microbunching instability is an ubiquitous problem in storage rings at high current density. However, the involved fast time-scales hampered the possibility to make direct real-time recordings of theses structures. When the structures occur at a cm scale, recent works at UVSOR [1], revealed that direct recording of the coherent synchrotron radiation (CSR) electric field with ultra-high speed electronics (17 ps) provides extremely precious informations on the microbunching dynamics. However, when CSR occurs at THz frequencies (and is thus out of reach of electronics), the problem remained largely open. Here we present a new opto-electronic strategy that enabled to record series of successive electric field pulses shapes with picosecond resolution (including carrier and envelope), every 12 ns, over a total duration of several milliseconds. We also present the first experimental results obtained with this method at Synchrotron SOLEIL, above the microbunching instability threshold. The method can be applied to the detection of ps electric fields in other situations where high repetition rate is also an issue
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