Fresnel reflections in inverse double freeform lens design.

In this paper we present a method for designing a double freeform lens that includes the effect of Fresnel reflections on the output intensity. We elaborate this method for the case of a point source and a far-field target. A new expression for the transmittance through a double freeform lens is derived, and we adapt a least-squares algorithm to account for this transmittance. A test case based on street lighting is used to show that our adaptation improves the accuracy of the algorithm and that it is possible to minimize Fresnel losses with this new method to design efficient lenses.

Computing aberration coefficients for plane-symmetric reflective systems: a Lie algebraic approach.

We apply the Lie algebraic method to reflecting optical systems with plane-symmetric freeform mirrors. Using analytical ray-tracing equations, we construct an optical map. The expansion of this map gives us the aberration coefficients in terms of initial ray coordinates. The Lie algebraic method is applied to treat aberrations up to arbitrary order. The presented method provides a systematic and rigorous approach to the derivation, treatment, and composition of aberrations in plane-symmetric systems. We give the results for second- and third-order aberrations and apply them to three single-mirror examples.

Fresnel reflections in inverse freeform lens design.

In this paper we propose a method to design a freeform lens including the effect of Fresnel reflections on the transmitted intensity. This method is elaborated for a lens with one freeform surface shaping a far-field target from a point source or collimated input beam. It combines the optical mapping with the energy balance incorporating the loss due to Fresnel reflections, which leads to a generalized Monge-Ampère equation. We adapt a least-squares solver from previous research to solve the model numerically. This is then tested with a theoretical example and a test case related to road lighting.

Alternative computation of the Seidel aberration coefficients using the Lie algebraic method.

We give a brief introduction to Hamiltonian optics and Lie algebraic methods. We use these methods to describe the operators governing light propagation, refraction, and reflection in phase space. The method offers a systematic way to find aberration coefficients of any order for arbitrary rotationally symmetric optical systems. The coefficients from the Lie method are linked to the Seidel aberration coefficients. Furthermore, the property of summing individual surface contributions is preserved by the Lie algebraic theory. Two examples are given to validate the proposed methodology with good results.

Design of a freeform two-reflector system to collimate and shape a point source distribution.

In this paper we propose a method to compute a freeform reflector system for collimating and shaping a beam from a point source. We construct these reflectors such that the radiant intensity of the source is converted into a desired target. An important generalization in our approach compared to previous research is that the output beam can be in an arbitrary direction. The design problem is approached by using a generalized Monge-Ampère equation. This equation is solved using a least-squares algorithm for non-quadratic cost functions. This algorithm calculates the optical map, from which we can then compute the surfaces. We test our algorithm on two cases. First we consider a uniform source and target distribution. Next, we use the model of a laser diode light source and a ring-shaped target distribution.

Generating-function approach for double freeform lens design.

Many LED lighting applications involve the design of multiple optical surfaces. A prime example is a single lens with two refractive surfaces. In this paper, we consider an LED light source approximated as a point and a far-field target intensity. Using Hamilton's characteristic functions, the design problem is converted into two generalized Monge-Ampère equations by deriving a generating function for each optical surface. The generating function is a generalization of the cost function in optimal transport theory. The generalized Monge-Ampère equations are solved using an iterative least-squares algorithm. To compute the first optical surface, we choose an intermediate far-field target intensity. By choosing different intermediate target intensities based on the source and target intensity, we develop a "knob" to distribute the refractive power over both surfaces of the lens. We apply the algorithm on two example problems and show it is capable of producing complicated target distributions.

Reliability of Repeated Measurements on Post-Burn Scars with Corneometer CM 825(®).

BACKGROUND/PURPOSE: The water content in burn scars, the parameter of stratum corneum water holding capacity, is an important feature in evaluation of biophysical properties of scars. Nevertheless, quantifiying this parameter is a challenge. In this study, the reliability of repeated water content measurements with Corneometer CM825(®) on (burn) scars was investigated. METHODS: Intra-observer reliability, inter-observer reliability and day-by-day variability were examined on 30 scars by means of intra-class correlation coefficient (ICC) and within-subject coefficient of variation (WSCV). Bland-Altman plots with '95% limits of agreement' were constructed. RESULTS: Results revealed excellent ICC values (ICCintra  = 0.985; ICCinter  = 0.984) with relatively low WSCV (WSCVintra  = 6.3%; WSCVinter  = 10.6%) for respectively intra- and inter-observer reliability. However, the Bland-Altman plot showed that more than 5% of differences were expected to exceed 4 a.u., the limit of what has been defined as a clinically acceptable difference. Results for day-by-day variability showed good ICC value (ICCday-by-day  = 0.849) and higher WSCV (WSCVday-by-day  = 20.5%). CONCLUSION: The Corneometer CM825(®) is an objective and sensitive instrument for water content measurements. On the basis of our results, we concluded that the instrument can be used in clinical trials, but only under very strict conditions with standardized test protocol, preferably in combination with the evaluation of other physiological parameters.

A prediction model for strike in the sheep nasal fly, Oestrus ovis, in Namibia.

A model was developed for predicting outbreaks of Oestrus ovis throughout the main sheep farming areas of Namibia. Pupal developmental periods were studied, concomitant air and soil temperatures enabling degree-day calculations to be made for prediction of adult fly strike. Monitoring of larval infection established seasonal incidence of O. ovis infestation and acted as verification of predictions. The establishment of relevant isothermal maps for Namibia made possible extrapolation from the several study sites to the entire sheep farming area. Retrospective and actual predictions of the important first peak after winter were considered accurate enough to recommend timing of control measures. No evidence of overwintering of first stage instars was found, the strategy used instead being extended pupation. Adult fly energy reserves were determined.

Arthropod parasites of springbok, gemsbok, kudus, giraffes and Burchell's and Hartmann's zebras in the Etosha and Hardap Nature Reserves, Namibia.

A total of 48 springbok, 48 gemsbok, 23 kudus and 6 giraffes were examined for ticks and lice, while 9 Burchell's zebras and 6 Hartmann's mountain zebras were examined only for ticks. Springbok and gemsbok were shot in both the Etosha National Park in the north and the Hardap Nature Reserve in the south of Namibia. All the other animals were shot in the Etosha National Park. A total of 7 ixodid tick species and 8 lice species were recovered. The springbok carried few ticks. The adults of a Rhipicephalus sp. (near R. oculatus) were most numerous on the gemsbok, especially during November. The kudus were the only animals harbouring Rhipicephalus zambeziensis. Adult Hyalomma truncatum, followed by adult Hyalomma marginatum rufipes, were most abundant on the giraffes and adult Rhipicephalus evertsi mimeticus were commonest on the zebras.

Cardiomyopathy caused by avocado (Persea americana Mill) leaves.

Six of 21 goats feeding on fresh avocado (Persea americana) leaves from pruned trees, showed clinical signs of cardiac distress. Some sheep subsequently dosed experimentally at different dosage rates with the same and other avocado varieties, showed clinical signs of respiratory or cardiac distress and myocardial lesions at autopsy.

Parasites of South African wildlife. II. Helminths of kudu, tragelaphus strepsiceros, from South West Africa/Namibia.

A total of 23 kudu, Tragelaphus strepsiceros, were shot at 2-month intervals from June 1983 to April 1984 in the Etosha Game Reserve in the north of South West Africa/Namibia. The parasite survey conducted on these animals yielded 2 cestode and 12 nematode species. Haemonchus vegliai and Cooperia neitzi were the most prevalent nematodes and occurred in 13 animals each, followed by Cooperia acutispiculum and an Onchocerca sp. (9 animals each). The remaining nematodes were present in 4 (17%) or fewer of the antelope. C. neitzi was the most numerous nematode, a total of 3,564 being recovered from all the antelope, followed by C. acutispiculum (2,552) and H. vegliai (1,050). Individual total worm burdens varied from 4-1,326 with 2 kudu harbouring no worms. The mean burden of 399 worms was considered negligible. A single kudu was shot in the Namib-Naukluft Park in the south of the country. This animal harboured no parasites.

The seasonal incidence of helminth parasites and of Oestrus ovis in Karakul sheep in the Kalahari region of South West Africa, Namibia.

The seasonal incidence of gastro-intestinal helminths and of Oestrus ovis was determined by slaughter of successive groups of 4 tracer lambs, each exposed on pasture for 33 days. Haemonchus contortus was present from March 1979 to early July 1979, with a generally increasing percentage of 4th stage larvae in each successive month. A "spring rise" in the egg count was seen in flock sheep in October 1978. Oesophagostomum columbianum was recovered from tracers slaughtered in March 1979. Apart from December and March, Moniezia spp. were present from November 1978 to early July 1979. Oestrus ovis was active from September 1978 to early June 1979, with peak larval burdens recorded from October to December and from April to early June.