Improved integrity algorithms for integrated GPS/INS systems in the presence of slowly growing errors

GPS is the most widely used satellite navigation system. By design, there is no provision for real time integrity information within the Standard Positioning Service (SPS). However, in safety critical sectors like aviation, stringent integrity performance requirements must be met. This can be achieved using special augmentation systems or at the user sensor level through Receiver Autonomous Integrity Monitoring (RAIM) or both. RAIM, which is considered as the most cost effective method relies on data consistency, and therefore requires redundant measurements for its operation. An external aid to provide this redundancy can be in the form of an Inertial Navigation system (INS). This should enable continued performance even during RAIM holes (when no redundant satellite measurements are available). However, the integrated system faces the risk of failures generated at different levels of the system, in the operational environment and at the user sensor (receiver) level. This thesis addresses integrated GPSIINS architectures, the corresponding failure modes and the sensor level integrity algorithms used to protect users from such failure modes. An exhaustive literature review is conducted to identify the various failure modes. These are then grouped into classes based on their characteristics and a mathematical (failure) model is specified for each class. For the analysis of failures, a simulation of a typical aircraft trajectory is developed, including the capability to generate raw measurements from GPS and the INS. The simulated GPS and INS measurements for the aircraft are used to evaluate the performance of the current integrity algorithms. Their performances are assessed for the most difficult case of failures; slowly growing errors (SGE), and shown to be inadequate (i.e. a considerable period of time is required for detection). This is addressed by developing a new algorithm based on the detection ofthe growth rate ofa typical test statistic (assuming a single failure at a time). Results show that the new algorithm detects slowly growing ramp-type errors faster than the current methods, with a forty percent improvement in the time it takes to detect the worst case SGE. The algorithm is then extended to include detection of multiple SGEs for which a new tightly coupled method referred to as the 'piggyback architecture' is proposed. This method provides the novel capability of detecting all failures including those affecting the INS. The proposed algorithms are validated with real GPS and INS data. In this way, the integrity performance of the integrated system is enhanced against the worst case failures with a detection time that is beneficial for the achievement of stringent time-to-alert requirements. A practical implementation would then comprise of the use of the rate detector algorithm alongside the current methods.Imperial Users onl

Demonstrating competence in endoscopic retrograde cholangiopancratico graphy (ERCP): Recently credentialed operator\u27s performance for deep biliary cannulation over 1 year period from a tertiary care hospital in Pakistan

Objective: To measure the success rate of endoscopic retrograde cholangiopancreaticography biliary cannulation of a recently credentialed endoscopist at a tertiary hospital.Methods: The clinical audit was conducted at the Aga Khan University Hospital. Karachi, and comprised data of all patients who underwent endoscopic retrograde cholangiopancreaticography under the care of a single operator during 2016. Data was retrospectively extracted from patient charts by an assistant blinded to the study. Data extracted included demographics, admission type, details and indication for the procedure, diagnosis, cannulation outcome, duct clearance, complications, follow-up surgical intervention, radiological imaging and mortality post-endoscopy. Data was analysed using SPSS 19.Results: Of 143 procedures performed, 102(71.3%) were included. The mean age was 52±17 years and 54(52.9%) of them were females. Most common indication was choledocholithiasis in 70(68.6%). The average procedure time was 41.5±5.5 minutes. Cannulation success rate was 96(94.1%). Complications included post-procedure pancreatitis in 5(4.9%), minimal bleeding in 8(7.8%) and oesophageal perforation in 1(0.98%). There was no procedure-related mortality.Conclusions: The success rate was high and complications were low with zero mortality

Pituitary Tuberculoma

Tuberculosis rarely involves the hypothalamo-pituitary region and constitutes only 1% of the lesions involving the sellar and/or suprasellar region. Coleman and Meredith first reported pituitary tuberculosis in 1940, and only a handful of cases have been reported ever since. It may manifest as a chiasmal syndrome due to compression of the optic chiasm or as hypopituitarism due to pituitary destruction. It has a characteristic radiological appearance and can mimic a pituitary adenoma. Diagnostic procedures, such as trans-sphenoidal biopsy, are crucial for accurate diagnosis. We report a case of a 32-year male, who presented with complaints of headache and decreased visual acuity for the past 6 months. Eye examination revealed bitemporal hemianopsia. Brain MRI scan showed a mass in the sella with features suggestive of pituitary adenoma. Transcranial resection of the mass was performed; histopathology of the excised mass proved it to be a pituitary tuberculoma

School-based injury outcomes in children from a low-income setting: results from the pilot injury surveillance in Rawalpindi city, Pakistan

Background School-based injuries account for one in five unintentional childhood injuries. Little is known about the epidemiology of school-based injuries in low-income settings. The objective of our study was to compare emergency department (ED) outcomes of the school-based injuries with respect to age, sex, and injury mechanisms in a Pakistani urban setting. Findings A pilot injury surveillance study was conducted at the EDs of three major tertiary-care hospitals of Rawalpindi city from July 2007 to June 2008 and included children of less than 15 years injured at school. The World Health Organization’s questionnaire for injury surveillance was used. There were 923 school injury cases. Mean age of children involved was 8.3 years (SD ± 3.3) with male female ratio 2.9:1. Most injuries occurred while playing 85.6% (n = 789); of which the most common mechanism was falls (n = 797, 86.4%). Nineteen of twenty cases were directly discharged home from the ED (N = 861). Compared to ED discharged cases, injury characteristics overrepresented in hospital admitted cases (n = 46) were age 10–14 years (65.2% vs. 40.9%, p = 0.005), male (88.6% vs. 25.9%), involved in educational activities (39.1% vs. 5.3%), injured from fire/heat (37.8% vs. 0.6%), had burns (39.5% vs. 0.9%) and head injuries (27.9% vs. 6.4%). Conclusion Falls while playing are the commonest injury mechanism in school-based injuries reported in our ED sample. School officials need to prevent these injuries. Studying injury hazards present in school environment in Pakistan might facilitate developing specific prevention strategies

Bomb blast in a tertiary care hospital, the challenges faced during management of victims in a resource limited country

Abstract Introduction: A bomb blast in a hospital results in a many fold increase in the casualties. The affected health care in the region is the next challenge faced by the administration of the city. We discuss the challenges faced after a bomb blast in the civil hospital of Quetta, Pakistan on 8 August 2016. Methods: A retrospective review of the medical records of patients who were transferred by air to the Aga Khan University Hospital Karachi over a period of 86 h after the blast in Quetta. Results: Seventy-five patients were received in three separate waves; those received in the first wave were sicker than the following waves. Errors in triage and communication which could have been prevented were identified. Conclusion: Security of hospitals needs to be improved to avoid such incidents in future. The teams involved in the management of these incidents should be trained about triage and communication and its importance. There is need for designated trauma centers to take care of these incidents

Prognostic factors in patients with salivary gland malignancy: A retrospective cohort study

Our objective was to determine the factors affecting the prognosis in patients with major salivary gland malignancy presenting to Aga Khan University Hospital in Karachi. Retrospective cohort study was carried out at our center on patients diagnosed and treated for salivary gland cancers. Presentation and treatment offered was reviewed from medical charts. Telephonic interviews were conducted to assess the survival of patients who were lost to follow-up. Log rank test was used to compare the mean survival times. A total of 36 patients were included in the study. The mean age was 45.1 +/- 14.6 years. Majority were male 21 (58.3%). The most common malignancy was mucoepidermoid carcinoma (36.1%) followed by adenoid cystic carcinoma (22.2%). Node positivity, grade of tumor, radiotherapy and chemotherapy were a significant indication of survival times on log rank test

Road traffic injuries in Rawalpindi city, Pakistan.

Data on road traffic accident (RTA) injuries and their outcome are scarce in Pakistan. This study assessed patterns of RTA injuries reported in Rawalpindi city using standard surveillance methods. All RTA injury patients presenting to emergency departments of 3 tertiary care facilities from July 2007 to June 2008 were included. RTA injuries (n = 19 828) accounted for 31.7% of all injuries. Among children aged 0-14 years females suffered twice as many RTA injuries as males (21.3% versus 11.4%), whereas this trend reversed for the age group 15-24 years (41.9% versus 21.7%). One-fifth of injuries were either fractures or concussion. Severity and outcome of injuries were worse for the age group 45 years and older. For every road traffic death in Rawalpindi city, 29 more people were hospitalized and 177 more received emergency department care. These results suggest the need for better RTA injury surveillance to identify preventive and control measures for the increasingly high road disease burden in this city