Quantifying numerical dispersion in non-orthogonal FDTD meshes

Numerical electromagnetic models such as FDTD are widely used for the design and analysis of structures, including antennas. Numerical dispersion is one of the main sources of error that degrade the accuracy of the results-for each structure of interest, the users of the model must attempt to generate a mesh that will avoid introducing high levels of dispersion. This is, however, especially difficult for non-orthogonal meshes since little information is available on the dispersion properties of the non-orthogonal FDTD algorithm on complex meshes. For the first time, the dispersion in realistic non-orthogonal FDTD models of microstrip structures is quantified directly through numerical simulations. A test structure is considered, discretised using a number of nonorthogonal mesh configurations, including single and multiple skew angles. A numerical analysis of reflections generated at the transition between two mesh regions with different skew angles is also presented. These results give a practical guide to mesh generation for users of the algorith

Modelling metallic discontinuities with the non-orthogonal finite difference time domain method

Numerical electromagnetic models, such as the finite difference time domain (FDTD) method, have many applications. The authors focus on the non-orthogonal FDTD method, which offers an improved geometric flexibility compared to other standard techniques. Results from numerical electromagnetic analysis methods, such as the FDTD method, are often degraded by an error known as numerical dispersion. For metallic structures this dispersion error is often higher than expected from theoretical considerations. The source of this additional error is due to the reciprocal field interpolation scheme used in the non-orthogonal FDTD algorithm. The error is illustrated by means of a microstrip waveguide and a microstrip antenna. Techniques for reducing this error are evaluated; careful construction of the mesh at the metallic boundary being the most reliable solution

Strengthening primary eye care in South Africa: An assessment of services and prospective evaluation of a health systems support package

Visual impairment is a significant public health concern, particularly in low- and middle-income countries where eye care is predominantly provided at the primary healthcare (PHC) level, known as primary eye care. This study aimed to perform an evaluation of primary eye care services in three districts of South Africa and to assess whether an ophthalmic health system strengthening (HSS) package could improve these services. Baseline surveys were conducted in Cape Winelands District, Johannesburg Health District and Mopani District at 14, 25 and 36 PHC facilities, respectively. Thereafter, the HSS package, comprising group training, individual mentoring, stakeholder engagement and resource provision, was implemented in 20 intervention sites in Mopani District, with the remaining 16 Mopani facilities serving as control sites. At baseline, less than half the facilities in Johannesburg and Mopani had dedicated eye care personnel or sufficient space to measure visual acuity. Although visual acuity charts were available in most facilities, <50% assessed patients at the correct distance. Median score for availability of nine essential drugs was <70%. Referral criteria knowledge was highest in Cape Winelands and Johannesburg, with poor clinical knowledge across all districts. Several HSS interventions produced successful outcomes: compared to control sites there was a significant increase in the proportion of intervention sites with eye care personnel and resources such as visual acuity charts (p = 0.02 and <0.01, respectively). However, engaging with district pharmacists did not improve availability of essential drugs (p = 0.47). Referral criteria knowledge improved significantly in intervention sites (p<0.01) but there was no improvement in clinical knowledge (p = 0.76). Primary eye care in South Africa faces multiple challenges with regard to organisation of care, resource availability and clinical competence. The HSS package successfully improved some aspects of this care, but further development is warranted together with debate regarding the positioning of eye services at PHC l

Risk profiles and one-year outcomes of patients with newly diagnosed atrial fibrillation in India: Insights from the GARFIELD-AF Registry.

BACKGROUND: The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) is an ongoing prospective noninterventional registry, which is providing important information on the baseline characteristics, treatment patterns, and 1-year outcomes in patients with newly diagnosed non-valvular atrial fibrillation (NVAF). This report describes data from Indian patients recruited in this registry. METHODS AND RESULTS: A total of 52,014 patients with newly diagnosed AF were enrolled globally; of these, 1388 patients were recruited from 26 sites within India (2012-2016). In India, the mean age was 65.8 years at diagnosis of NVAF. Hypertension was the most prevalent risk factor for AF, present in 68.5% of patients from India and in 76.3% of patients globally (P < 0.001). Diabetes and coronary artery disease (CAD) were prevalent in 36.2% and 28.1% of patients as compared with global prevalence of 22.2% and 21.6%, respectively (P < 0.001 for both). Antiplatelet therapy was the most common antithrombotic treatment in India. With increasing stroke risk, however, patients were more likely to receive oral anticoagulant therapy [mainly vitamin K antagonist (VKA)], but average international normalized ratio (INR) was lower among Indian patients [median INR value 1.6 (interquartile range {IQR}: 1.3-2.3) versus 2.3 (IQR 1.8-2.8) (P < 0.001)]. Compared with other countries, patients from India had markedly higher rates of all-cause mortality [7.68 per 100 person-years (95% confidence interval 6.32-9.35) vs 4.34 (4.16-4.53), P < 0.0001], while rates of stroke/systemic embolism and major bleeding were lower after 1 year of follow-up. CONCLUSION: Compared to previously published registries from India, the GARFIELD-AF registry describes clinical profiles and outcomes in Indian patients with AF of a different etiology. The registry data show that compared to the rest of the world, Indian AF patients are younger in age and have more diabetes and CAD. Patients with a higher stroke risk are more likely to receive anticoagulation therapy with VKA but are underdosed compared with the global average in the GARFIELD-AF. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01090362