Considerations on the Diffraction Limitations to the Spatial Resolution of Optical Transition Radiation

The interest in using optical transition radiation (OTR) in high energy (multiGeV) beam diagnostics has motivated theoretical and experimental investigations on the limitations brought by diffraction on the attainable resolution. This paper presents calculations of the diffraction effects in an optical set-up using OTR. The OTR diffraction pattern in a telescopic system is calculated taking into account the radial polarization of OTR. The obtained diffraction pattern is compared to the patterns obtained by other authors and the effects of different parameters on the shape and on the size of the OTR diffraction pattern are studied. The major role played by the radial polarization on the shape of the diffraction pattern is outlined. An alternative method to calculate the OTR diffraction pattern is also sketchedComment: Submitted to Particle Accelerator

Generation of circularly polarized photons for a linear collider polarized positron source

Various methods of obtaining longitudinally polarized positrons for future linear colliders are reviewed. Special attention is paid to the schemes using circularly polarized high-energy photons for positron production. Most effectively such photons are obtained from electrons passing through a helical undulator or colliding with a circularly polarized laser wave. Spectrum and polarization of radiation emitted during helical motion of electrons are considered in detail. A new simple presentation of known formulas is used to account for the influence of the wave intensity, of the electron-beam angular divergence, of the collimation of radiation, and of the lateral and temporal profiles of the laser bunch on the radiation properties.Comment: 16 pages, 6 figure

Comparison of theory with experiment for positron production from high-energy electrons moving along crystal axes

Various positron distributions are obtained using an approach developed earlier for the description of electron-photon showers in axially aligned single crystals. Based on these distributions, characteristics of the positron yield measured in recent experiments are calculated. Theoretical estimations display a rather good agreement with experimental results obtained using 3 to 10 GeV electrons aligned to the - axis of the tungsten crystals.Comment: 10 pages, 6 Postscript figure

The Intellectual Contributions of American Muslim Scholars

This chapter discusses the work of five American Muslim scholars: Fazlur Rahman, Amina Wadud, Taha Jabir al-Alwani, Abdullahi Ahmed an-NaÊ¿im, and M. A. Muqtedar Khan. Their contributions influence and inform the debates on a variety of issues, such as ijtihad, shari\u27a, gender equality, human rights, democracy and reform, and interfaith dialogue. These scholars agree that a crisis of thought exists in the Muslim world and that it was created because of the absence of ijtihad. They recognize that many problems plague the Muslim world and Muslim communities ”problems partly engendered by taqlid and a reliance on old interpretations of the Qur\u27an. To solve them and achieve reform, justice, and gender equality, Muslim scholars should drive these debates forward through a commitment to continuous and progressive exegetical exercises. Thus this chapter outlines how each one of these five scholars explains and interprets these debates and assesses their attempts at reopening the doors of ijtihad

Kyste hydatique pancréatique: à propos d’un cas

La localisation pancréatique du kyste hydatique est rare, même dans les pays ou la maladie hydatique sévit à l'état endémique. Il ne représentant que moins de 1% de l'ensemble des localisations .La symptomatologie souvent insidieuse après une longue évolution, dépend du siège du kyste hydatique, ce qui peut expliquer les difficultés du diagnostic, prêtant à confusion avec les autres lésions kystiques du pancréas. Elle touche exceptionnellement l'enfant. Nous rapportons une observation survenue chez une patiente de 20 ans, victime il y'a 3 ans d'un traumatisme fermé de l'abdomen, qui présentait depuis 2 mois des épigastralgies isolées, avec ictère. A travers cette observation et une revue de la littérature, nous discutons les difficultés diagnostiques et les modalités du traitement chirurgical de cette localisation inhabituelle de la maladie hydatique

Polarized Positron Source with a Compton Multiple Interaction Point Line

ISBN 978-3-95450-115-1International audiencePositron sources are critical components of the future lepton colliders projects. This is essentially due to the high luminosity required, orders of magnitude higher than existing ones. In addition,polarization of the positron beam rather expands the physics research potential of the machine by increasing the precision of the measurements and enhancing certain types of interactions. In this framework, the Compton sources for polarized positron production are taken into account where the high energy gamma rays are produced by the Compton scattering and subsequently converted in the polarized electron-positron pairs in a target. The Compton multiple IPs line is proposed as one of the solutions to increase the number of captured positrons. This allows a significant increase in the emitted gamma ray flux impinging on the target. The gamma ray production with the Compton multiple IPs line is simulated and used for polarized positron generation. Later, a capture section based on an adiabatic matching device followed by a pre-injector linac is simulated to capture and accelerate the positron beam. The results obtained are presented and discussed

HIGH PULSED CURRENTS FROM PHOTO-FIELD EMITTERS

Différent microemitters - single or arrays - with various geometries and kinds of material have been irradiated with pulsed laser beams. These emitters working in photo-field emission regime delivered very high intensity electron bunches. Peak intensities as high as some tens of Amps with less than one ns duration have been obtained with U.V. light. New type of microemitters developed in collaboration with BNL have been tested since last year showing the possibility of obtaining charges above 20 nC with low energy laser puises, (εi = 100µJ). The main parameters affecting the choice of these emitters as quantum yield, photocurrent density, electron pulse length, repetition rate and vacuum system level are here discussed. Good performances obtained with these emitters as well as the absence of cesiation make these microemitters interesting candidates for the new generation of linac injectors as well as for multimegawatt RF sources. At LAL, Orsay efforts have been made since three years to develop such electron sources

An unusual crossed course of separately originating left circumflex and left anterior descending arteries with concomitant anomalies found in multi-slice computed tomography

Coronary artery anomalies occur in approximately in 1-2% of the population. The split origin of branches of the left coronary artery is a relatively common anomaly, usually with no significant observable impairment of cardiac function. The application of multi-slice computed tomography (MSCT) for cardiac imaging is increasing and becoming, along with other techniques, a recognised method of examination of the coronary arteries. In the case presented we observed in an ECG-gated MSCT the anomalous origin and proximal course of the arteries of the left sinus of Valsalva. The ostiae of both coronary arteries were located unusually: the ostium of the LAD was found posterior to the ostium of the LCx. Because of this, the proximal part of the LAD crossed the proximal part of the LCx superiorly. Furthermore, muscular bridges were found in the middle part and in the first diameter branch of the LAD. To our knowledge, this is the first case of a crossed course of the LCx and the LAD to be presented in the literature. Applications of MSCT in coronary imaging are presented in comparison with other diagnostic imaging methods. The advantages and limitations of MSCT as a diagnostic tool for anomalies of the coronary arteries are discussed