Retropharyngeal abscesses are rare in adults. They occur mostly in immunocompromised patients or as a foreign body complication. We report 5 cases of retropharyngeal abscess collected in the ENT Department of CHU Mohammed VI of Marrakech, during a two-year period (December 2008 to December 2009). Local trauma by foreign body ingestion was the aetiology in four patients. The presenting symptoms, for all patients, were fever, odynophagia, torticollis, and trismus, and the clinical examination showed bulging of the posterior wall of the oropharynx. The radiography of cervical spine showed prevertebral thickening in all cases, this thickening was associated with an aspect of vertebral lysis of the fourth cervical vertebra in one case. A CT scan was performed in all our cases and showed features of retropharyngeal abscess which was associated, in one case, with spondylodiscitis. The biological assessment found one case of diabetes. The intradermal reaction to the tuberculin was clearly positive in one case. Endobuccal abscess puncture was practiced in 4 cases; only one organism was identified by culture: Staphylococcus aureus treatment was based on triple intravenous antibiotics and anti-Koch's therapy (in one case), and the surgical drainage under general anesthesia was also performed in the case of the diabetes patient which required also the correction of hyperglycemia in intensive care unit. The outcome was good in all our patients. The diagnosis of retropharyngeal abscess can be difficult and one must seek a comorbidity; a tuberculosis aetiology must be considered in countries with a high prevalence. The management of these cases is based on antibiotics and surgical drainage.

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Running rails are used as the return path for the train current in most DC electrified rail transit systems. The resultant rail voltage causes stray current to return to the DC supply source via other paths, such as nearby metallic infrastructure. Stray current is the main cause of corrosion in metallic parts located in the railway proximity. This study reviews various earthing schemes including thyristor earthed, diode earthed, floating and solidly earthed and corrosion phenomenon in DC railway traction systems. Then, based on simulations, a comparative study of safety and corrosive effects of the stray current, produced by various earthing schemes is presented. The study is part of the concept designed to control the stray current at Tehran Metro Line 3. Results of the study have been validated by simulation studies using a multi-train simulation software tool and the system data from Tehran Metro Line 3. The study shows some interesting findings such as corrosion damage increases near traction substations.

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The neutral wire in most existing power flow and fault analysis software is usually merged into phase wires using Kron's reduction method. In some applications such as fault analysis, fault location, power quality studies, safety analysis, loss analysis, etc., knowledge of the neutral wire and ground currents and voltages could be of particular interest. In this paper, a general short circuit analysis algorithm for three-phase four-wire distribution networks, based on the hybrid compensation method, is presented. In this novel use of the technique, the neutral wire and assumed ground conductor are explicitly represented. A generalized fault analysis method is applied on the distribution network for conditions with and without embedded generation. Results obtained from several case studies on medium and low voltage test networks, with unbalanced loads, for isolated and multi-grounded neutral scenarios, are presented and discussed. Simulation results show the effects of neutrals and system grounding on the operation of the distribution feeders.

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