Simulation Study on Effects of Order and Step Size of Runge-Kutta Methods that Solve Contagious Disease and Tumor Models.

Biological processes such as contagious disease spread patterns and tumor growth dynamics are modelled using a set of coupled differential equations. Experimental data is usually used to calibrate models so they can be used to make future predictions. In this study, numerical methods were implemented to approximate solutions to mathematical models that were not solvable analytically, such as a SARS model. More complex models such as a tumor growth model involve high-dimensional parameter spaces; efficient numerical simulation techniques were used to search for optimal or close-to-optimal parameter values in the equations. Runge-Kutta methods are a group of explicit and implicit numerical methods that effectively solve the ordinary differential equations in these models. Effects of the order and the step size of Runge-Kutta methods were studied in order to maximize the search accuracy and efficiency in parameter spaces of the models. Numerical simulation results showed that an order of four gave the best balance between truncation errors and the simulation speed for SIR, SARS, and tumormodels studied in the project. The optimal step size for differential equation solvers was found to be model-dependent.

Continuous rise of urinary iodine excretion and drop in thyroid gland size among adolescents in Mecklenburg-West-Pomerania from 1993 to 1997.

Improved legislation (1989, 1993), as well as education of the public, are likely to improve the iodine supply for the German population. Children and adolescents will be the first to profit. We investigated thyroid size and urinary iodine excretion in a total of 2906 students aged 10 to 18 in Mecklenburg-West-Pomerania in 1993, 1995, and 1997. The median urinary iodine excretion rose from 73 microg/g creatinine in 1993 to 133 microg/g in 1997. The prevalence of goiter, according to the reference range of Gutekunst, dropped from 33% to 10% over the same interval, and the median thyroid size declined from 11 ml to 6 ml. While only 6% of the test subjects excreted more than 150 microg iodine per g creatinine in 1993, this figure rose to 33% in 1997. The improved alimentary iodine supply is due to the increased use of iodine enriched salt by the food industry, food factories and in common food supply services.

[Increased dietary intake of iodine in young people in Mecklenburg-Vorpommern 1993 and 1996]. / Alimentäre Jodaufnahme bei Jugendlichen in Mecklenburg-Vorpommern zwischen 1993 und 1996 gestiegen.

We investigated the goiter prevalence and the urinary iodine excretion of 2,109 young people between 10 and 18 years in the district of Mecklenburg-Vorpommern, Germany in 1995/96. The thyroid volume was determined by ultrasound (7.5 MHz), the iodine excretion by a modified cer-arsenit method. The daily iodine excretion as related to the body surface area and the age related creatinine excretion per 24 h were measured. The results were compared with those of a similar study from 1993 in the same region and the same range of age. The goiter prevalence in 1997 amounted to 18.5%. Among the studied persons 3.6% showed one or more nodules within their thyroid gland. The iodine excretion increased from 70 micrograms in 1993 to 95 micrograms in 1997. There were no changes in the individual nutritional habits (especially iodine-containing foods, using iodized salt etc.). We believe that the raised iodine intake is the result of a higher iodine supply in the commercially produced foodstuffs and animal products due to an increased incorporation of iodine in manufacture of food products.

[Current state of alimentary iodine deficiency in Germany]. / Aktueller Stand der alimentären lodversorgung in Deutschland.

Germany finds itself among the most iodine deficient countries of Europe. Voluntary use of iodized salt constitutes the only goiter prophylaxis. In the last few years, measures such as the opening up of European internal markets, abolition of lac pertaining to the alimentary iodine consumption. Random samples of urine collected from 5932 persons without thyroid ailment, distributed over 32 regions of Germany, were measured for iodine excretion. The median value of iodine excretion was 72.4 micrograms I/g creatinine. Children under 10 years (76.9) and persons over 70 years (80.7) showed a slightly higher iodine elimination than those between 11-70 years (71.9). No differences between the former East Germany and West Germany as well as North, South and middle regions of unified Germany were observed. 55% of the study population presented with iodine values between 50 and 100 micrograms, 19% with lower than 50 micrograms. Only 9% showed sufficient iodine state. The results expose the inadequacy of the voluntary measures to tackle the problem of alimentary iodine deficiency.