Experimental demonstration of energy-chirp control in relativistic electron bunches using a corrugated pipe.

The first experimental study is presented of a corrugated wall device that uses wakefields to remove a linear energy correlation in a relativistic electron beam (a "dechirper"). Time-resolved measurements of both longitudinal and transverse wakefields of the device are presented and compared with simulations. This study demonstrates the feasibility to employ a dechirper for precise control of the beam phase space in the next generation of free-electron-lasers.

[Prevalence of dental caries among 12-year old schoolchildren in the Dakar region]. / Prévalence de la carie dentaire chez les élèves de 12 ans de la région de Dakar.

Oral diseases are considered as major public health problem. Dental caries restricts the school activities and are the dominant cause of dental morbidity. The aims of this survey were to determine prevalence of dental caries among pupils of Dakar and to study their food habits and oral hygiene. A descriptive transversal study was conducted from February 15th to May 07th, 2011 with respect of WHO directives (protocol of 1997) readjusted to Senegalese context. Our results showed a prevalence of 41.8%; a mean DMF index of 0.644; a proportion of teeth decayed of 65%, 32.2% for missing teeth and 2.7% of filled teeth. The multivariate logistic regression analysis showed that snacking, consumption of sweetened drinks far from meals and brushing teeth before the meals were significantly linked to the presence of dental caries. These results showed that the state of oral health and the prevention level of dental caries among these children were not so good. A new orientation of oral health policy based on messages regarding the main etiologic factors is imperative.

[Radiographic study of the canal anatomy of mandibular premolars in a Senegalese population]. / Etude radiographique de l'anatomie canalaire des premolaires mandibulaires dans une population Senegalaise.

AIM: The purpose of this study was to assess the canal anatomy of mandiblar premolars in Senegalese population. MATERIALS AND METHODS: Retroalveolar radiographs of mandibular premolars of 208 patients in Senegal were obtained. Two experienced practitioners using a long cone tube and the parallel plane technique with angulators took the radiographs. The canal morphology of each tooth was determined in terms of the number of canals radiologically visible to the apex. Any anatomic structure emanating from the pulp chamber or the principal canal to the apex and measuring more than 3 millimetres was considered to be a supplementary canal. RESULTS: For the 208 patients studied, 412 first premolars were present and 4 were absent.Among the 412 teeth, 335 (81.3%) had a single canal, 62 (15.1%) 2 canals, and 17 (3.6%) 3 canals. For the second premolars 408 were present. Of the 408 teeth, 352 (86%) had one canal, 49 (12%) 2 canals, and 8 (2%) 3 canals. CONCLUSION: The prevalence of two or more canals in premolar mandibular from Senegalese patients was similar to that found in the others ethnic population.

[Evaluation of the canal shaping duration with Pro Taper: 50 cases--clinical experience]. / Article original evaluation de la duree de preparation canalaire au Pro Taper: experience clinique a propos de 50 cas.

INTRODUCTION: Shaping canal is one of the most important steps in endodontic treatment. It allows the cleaning solutions to reach the totality of the canal and to control any infection of the canal system. To achieve this goal is not without difficulty with the steel instruments, because of their rigidity. Recently, the Nickel Titanium instruments were introduced in Endodontics, to allow a setting form technically simplified and faster The aim of this study was to evaluate the duration of the canal shaping with the Pro Taper system. MATERIALS AND METHODS: This exploratory study was carried out in Conservative Odontology and Endodontics service (OCE) of the department of Odontology of Faculty of Medicine, Pharmacy and Odonto-Stomatology of the University CheikhAnta Diop of Dakar in 2006. Sixty nine root canals (50 teeth) were shaped with ProTaper. RESULTS: The results showed that an average time of 17.35 minutes was necessary for the shaping of the long canals against 15.38 minutes for the middle canals and 14.29 minutes for the short canals. The average duration of canal shaping of the one-root teeth is 13.76 minutes and 17.77 minutes for the plural root teeth. CONCLUSION: Taking into account the necessity of maintaining the teeth on the arcade during long year; include that we have now to respect imperatively the biological principles during the canal shaping in a restricted duration to realize a dense and hermetic canal obturation of the canal system in the same meeting. The Pro Taper system is so a reliable means.

[Prevalence of fixed prosthesis-related periodontitis in Senegal]. / Prévalence de la prothèse fixèe et des parodontites apicales associées au Sénégal.

The purpose of this study was to determine radiographically the prevalence of periapical periodontitis in teeth restored with crown in a Senegalese population. Full mouth periapical radiographs were obtained from 208 consecutive adult patients (6234 teeth) presenting as new patients to the Dental Service of the University. The presence of crown restorations, the periapical status and technical quality of root fillings associated were evaluated. 7.69% (n = 16) of patients had at least one tooth that was crowned. The total number of crowns assessed was 0.95% (n = 59). The molars were the teeth most crowned 40.67% (n = 24) followed by anterior teeth 30.50% (n = 18) and premolars 28.81% (n = 17). All the crowned teeth had previous root canal treatment of which only 16.94% (n = 10) were acceptable. 53 % (n = 32) of the teeth had apical periodontitis (PAI > 2). Unacceptable root fillings were associated with a higher prevalence of periapical disease (p < 0.05). Crown with a post extending more than 4 millimetres from the apex were associated with more periapical lesions 64.28% (p < 0.05). The results indicate a low prevalence of crowned teeth, an absence of vital preparation, a high prevalence of radiographic periapical disease and unacceptable root fillings associated.

[Presence of yeasts in primary endodontic infections and study of their susceptibility to disinfection with sodium hypochlorite at 2.5]. / Recherche de levures dans les primo-infections endodontiques et étude de leur sensibilité à une désinfection à l'hypochlorite de sodium à 2,5.

INTRODUCTION: Endodontic infections are characterized by their microbial polymorphism with the presence of pathogenic agents such as bacteria. The aim of this study was to investigate the presence of yeast in the root canals of teeth with pulp necrotic with or without apical periodontitis and to study the sensibility of these at disinfection at sodium hypochlorite to 2.5 %. METHODS: Root canal samples, taken with paper points before and after disinfection with sodium hypochlorite dosed at 2.5 % on 50 single rooted teeth in 38 patients, were seeded in petri dishes containing Sabouraud Chloramphenicol (SC) (Conda Laboratories, Madrid). These stains were incubated in an incubator at 37°C for 48hours. The presence of yeast was confirmed by white colonies on the entire circumference of the tip paper. The identification of species was done by macroscopic and microscopic examinations associated with Blastese test. RESULTS: The yeast colonies were isolated from 7 teeth (14 %) out of 50. All positive samples were from teeth with an open necrotic pulp (P<0.001). The only species found was Candida albicans. Immediate disinfection with sodium hypochlorite at 2.5 % did not show a complete elimination of yeasts. CONCLUSION: The results of this study show that the canal of necrotic teeth with or without apical periodontitis may shelter yeasts even after immediate disinfection with sodium hypochlorite 2.5 %.

[Efficacy of sodium hydroxide at 2.5 %, chlorhexidine gluconate at 0.5 % and calcium hydroxide against Candida albicans]. / Étude de l'efficacité de l'hypochlorite de sodium à 2,5 %, de la chlorhexidine à 0,5 %, et de l'hydroxyde de calcium sur Candida albicans.

INTRODUCTION: Endodontic flora is dominated in the apical part of the channels by strict anaerobic and some facultative anaerobic bacteria but also by Candida yeasts, especially Candida albicans species that are involved in the maintenance and persistence of endodontic infections. Their elimination of the canal system in practice by chemo-mechanical methods of disinfection is not always guaranteed. Thus, this in vitro study was performed to determine the sensitivity of C. albicans with sodium hypochlorite (NaOCl) dosed at 2.5 %, the chlorhexidine digluconate 0.5 % and calcium hydroxide used in inter-session medication. METHODS: The diffusion method was used initially to test the sensitivity of C. albicans strains with the above products. Then a dilution technique has allowed us to determine the minimum inhibitory concentration of these active products on C. albicans. RESULTS: Strains from infected pulp teeth of patients showed a sensitivity of C. albicans to sodium hypochlorite to a minimum inhibitory concentration less than 70µg/mL and 30µg/mL for chlorhexidine. CONCLUSION: This study demonstrated a sensitivity of C. albicans to sodium hypochlorite and chlorhexidine.

Femtosecond and subfemtosecond x-ray pulses from a self-amplified spontaneous-emission-based free-electron laser.

We propose a novel method to generate femtosecond and subfemtosecond photon pulses in a free-electron laser by selectively spoiling the transverse emittance of the electron beam. Its merits are simplicity and ease of implementation. When the system is applied to the Linac Coherent Light Source, it can provide x-ray pulses the order of 1 fs in duration containing about 10(10) transversely coherent photons.

Future possibilities of the Linac Coherent Light Source.

A study of the potential for the development of the Linac Coherent Light Source (LCLS) beyond the specifications of the baseline design is presented. These future developments include delivery of X-ray pulses in the 1 fs regime, extension of the spectral range, increase of the FEL power, exploitation of the spontaneous emission, and a more flexible time structure. As this potential is exploited, the LCLS can maintain its role as a world-leading instrument for many years beyond its commissioning in 2008 and initial operation as the world's first X-ray free-electron laser.

Achievement of ultralow emittance beam in the accelerator test facility damping ring.

For high luminosity in electron-positron linear colliders, it is essential to generate low vertical emittance beams. We report on the smallest vertical emittance achieved in single-bunch-mode operation of the Accelerator Test Facility, which satisfies the requirement of the x-band linear collider. The emittances were measured with a laser-wire beam-profile monitor installed in the damping ring. The bunch length and the momentum spread of the beam were also recorded under the same conditions. The smallest vertical rms emittance measured at low intensity is 4 pm at a beam energy of 1.3 GeV, which corresponds to the normalized emittance of 1.0x1.0(-8) m. It increases by a factor of 1.5 for a bunch intensity of 10(10) electrons. The measured data agreed to the calculation of intrabeam scattering within much better than a factor of 2.

Extremely low vertical-emittance beam in the accelerator test facility at KEK.

Electron beams with the lowest, normalized transverse emittance recorded so far were produced and confirmed in single-bunch-mode operation of the Accelerator Test Facility at KEK. We established a tuning method of the damping ring which achieves a small vertical dispersion and small x-y orbit coupling. The vertical emittance was less than 1% of the horizontal emittance. At the zero-intensity limit, the vertical normalized emittance was less than 2.8 x 10(-8) rad m at beam energy 1.3 GeV. At high intensity, strong effects of intrabeam scattering were observed, which had been expected in view of the extremely high particle density due to the small transverse emittance.