We present a general finite-element solver, escript, tailored to solve geophysical forward and inverse modeling problems in terms of partial differential equations (PDEs) with suitable boundary conditions. Escript's abstract interface allows geoscientists to focus on solving the actual problem without being experts in numerical modeling. General-purpose finite element solvers have found wide use especially in engineering fields and find increasing application in the geophysical disciplines as these offer a single interface to tackle different geophysical problems. These solvers are useful for data interpretation and for research, but can also be a useful tool in educational settings. This paper serves as an introduction into PDE-based modeling with escript where we demonstrate in detail how escript is used to solve two different forward modeling problems from applied geophysics (3D DC resistivity and 2D magnetotellurics). Based on these two different cases, other geophysical modeling work can easily be realized. The escript package is implemented as a Python library and allows the solution of coupled, linear or non-linear, time-dependent PDEs. Parallel execution for both shared and distributed memory architectures is supported and can be used without modifications to the scripts.

Escript is a programming tool for implementing mathematical models in python using the finite element method (FEM). As users do not access the data structures it is very easy to use and scripts can run on desktop computers as well as highly parallel supercomputer without changes. Application areas for escript include earth mantle convection, geophysical inversion, earthquakes, porous media flow, reactive transport, plate subduction, erosion, and tsunamis.

The triangular quadrotor is a novel, more efcient conguration of quadrotor aircraft that uses a single large central rotor for lift and three smaller rotors for counter-torque and manoeuvering. Early experiments exhibited a precession eect due to the uncompensated gyroscopics of the main rotor. In this paper we discuss two techniques to x this problem: feedback linearisation and a mechanical apping joint. Simulations indicate that, contrary to expectations, feedback linearisation is not viable due to delays in the control system. The rotor apping approach is shown to be a more eective solution, both in simulation and ight experiments.

BACKGROUND:Lymphobronchial tuberculosis (TB) causes airway compression in 38% of patients. The airway obstruction is conventionally assessed with fibreoptic tracheobronchoscopy (FTB). Multidetector-row spiral computed tomography (MDCT) with three-dimensional volume rendering (3-D VR) has significantly improved the imaging of the airways. No previous studies have assessed the accuracy of 3-D VR in determining the degree of airway compression in children due to TB lymphadenopathy.OBJECTIVE:To compare 3-D VR CT to FTB for the assessment of airway compression due to TB lymphadenopathy in children.MATERIALS AND METHODS:Included in the study were 26 children presenting with symptoms of airway compression caused by pulmonary TB. MDCT of the chest and FTB were performed in all patients. Retrospective 3-D VR reconstruction of the major airways was performed from the original CT raw data and used to evaluate the tracheobronchial tree for site and degree of airway compression and then compared to the FTB findings. FTB was used as the reference standardRESULTS:By FTB 87 sites of airway compression were identified. Using the 3-D VR technique, 138 sites of airway compression were identified, of which 78 (90%) matched with the sites identified by FTB. The sensitivity and specificity of 3-D VR when compared with that of FTB was 92% and 85%, respectively. In four patients (15%), severe narrowing of the bronchus intermedius made FTB evaluation of the right middle and right lower lobe bronchi impossible. VR demonstrated significant distal obstruction in three of these four patientsCONCLUSION:3-D VR demonstrates a very good correlation with FTB in determining airway compression caused by TB lymphadenopathy in children. In combination with FTB, 3-D VR adds confidence to the bronchoscopy findings and complements FTB by adding additional information on the status of the airway distal to severe obstructions unreachable by FTB.

Infection of the lungs and airways by viral, bacterial, fungal and protozoal agents, often producing atypical radiographic features, is common in children with human immunodeficiency virus (HIV) infection. Conventional chest radiography and chest CT remain the most useful imaging modalities for evaluation of the immunocompromised patient presenting with a suspected pulmonary infection. In this review the radiological features of acute lung infections in this population are discussed.

Vertically transmitted HIV infection is a major problem in the developing world due to the poor availability of antiretroviral agents to pregnant women. HIV is a neurotrophic virus and causes devastating neurological insults to the immature brain. The effects of the virus are further compounded by the opportunistic infections and neoplasms that occur as a result of the associated immune suppression. This review focuses on the imaging features of HIV infection and its complications in the central nervous system.

OBJECTIVE:The incidence of tuberculosis (TB) is increasing in both developing and developed worlds, and children, in particular, represent a high-risk group for acquiring the disease. TB of the central nervous system is the most severe, life-threatening form of TB in infants and children. Approximately 10% of all patients with TB have central nervous system involvement.MATERIALS AND METHODS:We have selected four pediatric cases of unusual spinal TB that presented to our institution during the last 5 years. These include TB arachnoiditis, intramedullary spinal cord tuberculoma, TB spondylitis of the odontoid peg, and one child with tuberculous extradural abscess.CONCLUSION:TB may involve the intramedullary, extramedullary intrathecal compartment, or the extrathecal vertebral compartment in the form of an arachnoiditis, abscess, and spondylitis, respectively, often with unusual imaging presentations.

Background Pulmonary involvement in Kaposi sarcoma is rare in children and can be difficult to distinguish from other pathology. Objective To describe the radiological findings in paediatric pulmonary Kaposi sarcoma. Materials and methods Sequential chest radiographs of six children and CT scans of four of these children were evaluated retrospectively. Their ages ranged from 18 months to 10 years; four were male and two were female. All six children were HIV-positive. The observers were two radiologists. Results Chest radiographs revealed air-space (100%) and reticular (83%) opacification in the mid- and lower lung zones; pleural effusions were present in 83% of the children. All the children showed progressive air-space opacification on follow-up radiography. CT demonstrated bilateral air-space opacification in a perihilar distribution in all the children; reticular opacification was seen in 75%. All the children had mediastinal and axillary lymphadenopathy; 75% had bilateral hilar lymphadenopathy. Conclusion In both adults and children, chest radiography demonstrates perihilar and lower zone involvement. Pleural effusions are more common on radiographs in children. Air-space disease and lymphadenopathy are much more common on CT in children than adults.

The SA Journal of Radiology is the official journal of the Radiological Society of South Africa and the Professional Association of Radiologists in South Africa and Namibia. The SA Journal of Radiology is a general diagnostic radiological journal which carries original research and review articles, pictorial essays, case reports, letters, editorials, radiological practice and other radiological articles.

We present a series of 6 patients with physeal bars as a result of infection (predominantly meningococcal) demonstrating the typical MRI features of this entity and an explanation of how these features affect the choice of management.

Background. Extradural spinal cord compression in children may be the result of infection / inflammation or neoplasia. It is vital to differentiate between the two as there is considerable difference in the management of these entities. Objective. The aim of this paper is to determine whether there are significant differences between TB spondylitis and neoplasia causing extradural compression of the cord with regard to the anatomical distribution and compartmentalisation. Materials and methods. A group of 16 children between the ages of 4 months and 14.2 years who had magnetic resonance (MR) evaluation of the spine consecutively were analysed retrospectively. Results. A wide variety of neoplasms demonstrated an anatomical site and compartment on MRI that is 'characteristic' of TB spondylitis. Conclusion. Anatomical distribution alone does not assist in narrowing the differential diagnosis. There is still need for biopsy in children with extradural compression by a mass.

Paragangliomas of the head and neck are ubiquitous in their distribution, originating from the paraganglia or glomus cells within the carotid body, vagal nerve, middle ear, jugular foramen and numerous other locations. 1 Imaging studies depict the location and extent of tumour involvement, help determine the surgical approach and help predict operative morbidity and mortality. The imaging features of common paragangliomas of the head and neck are illustrated in this article.

Background Intracranial tuberculous ( TB) abscesses still cause a diagnostic dilemma on both CT and MRI as they may mimic neoplasms. Recognition of TB abscesses may prompt further imaging and appropriate trial of therapy, and may reduce the need for biopsy.Objective To report the CT features of eight intracranial TB lesions in children initially diagnosed as neoplasms and eventually treated as TB abscesses.Materials and methods We undertook a 3-year retrospective review of children with an initial CT diagnosis of intracranial neoplasm who were subsequently diagnosed as having TB abscesses.Results Eight patients out of 60 with an initial diagnosis of a neoplasm on CT were misdiagnosed and were ultimately determined to have TB abscesses after biopsy or a trial of anti-TB therapy. The most consistent constellation of findings for the lesions were low density (n=5), ring enhancement (n=8), cerebral hemisphere location (n=7), mass effect (n=6), surrounding oedema (n=5) and absence of a soft-tissue-density mass ( n=8).Conclusion In endemic regions, intracranial lesions with these appearances on CT should undergo further imaging and possibly a trial of anti-TB therapy before considering biopsy.

BACKGROUND:Focal basal meningeal enhancement may produce a confusing CT picture in children with suspected tuberculous meningitis (TBM).OBJECTIVE:To demonstrate the incidence, distribution and appearance of localized basal meningeal enhancement in children with TBM.MATERIALS AND METHODS:CT scans of patients with definite (culture proven) and probable (CSF suggestive) TBM were retrospectively evaluated by two observers. Localized basal enhancement was documented as involving: unilateral cistern of the lateral fossa (CLF), unilateral sylvian fissure, unilateral CLF and sylvian fissure in combination, unilateral CLF and sylvian fissure with ipsi- or contralateral ambient cistern and isolated quadrigeminal plate cistern.RESULTS:The study included 130 patients with TBM (aged 2 months to 13 years 9 months). Focal basal enhancement was seen in 11 patients (8.5%). The sylvian fissure was involved most commonly, followed by the lateral fossa cistern. The ambient cistern was involved in three patients and the quadrigeminal plate cistern in one. Focal areas of enhancement corresponded to the areas of infarction in every patient.CONCLUSION:Focal basal meningeal enhancement is common (8.5%) in paediatric TBM. This must be kept in mind when evaluating CT scans in children presenting with focal neurological findings, seizures or meningism in communities where TBM is endemic.