This brief tutorial will get you acquainted with the MERLIN-Expo user interface and philosophy. We will cover the different steps taken when using MERLIN-Expo for a study, from setting up the model to entering data to running simulations to inspecting results.
For this tutorial we will study acute lead poisoning of children. A family with a 4 year old daughter are re-painting their house. The daughter sits on the ground and eats paint chips that she finds in the grass.
What makes MERLIN-Expo unique is its flexibility. MERLIN-Expo ships with a library of sub-systems that you can combine to quickly create a model for a specific scenario. In this example we need only one sub-system - a human sub-system.
The model screen displays the (mathematical) model for your study. As you have chosen a blank template, it is initially empty.
The library is accessed by right-clicking the white area and choosing Add from library… from the menu that appears.
A box for a human being should now appear. To look inside the box, either
To see the equations used in the model you need the information panel.
The information panel should now display information about the selected object. You can click anything in blue to navigate between the model objects.
A description of this option is now presented on the right hand side. This option allows you to specify which route a contaminant takes when being ingested. As different contaminants can take different route, you need to select Lead from the drop down list.
Lead can enter the body either via inhalation or via ingestion. The time series screen let you enter time dependent inputs to the model. These are typically measurements (concentrations, rain, temperature, etc.).
Time series' always start at day 0 (because this is when the simulation is set to start).
We want to enter a step function for ingestion were the kid eats 1 grams of lead during a 24 hour period:
|Time (d)||Value (mg/d)|
The Editor below should now display a curve with a peak at day 0. The x-axis shows the full time span of the simulation, which by default is 365 days. You should zoom in to make sure everything looks ok:
When looking closely, you should see that the curve is actually not a step - it is a tilted line. This is because the ingestion rate data is linearly interpolated.
Values which remain constant during the simulation are entered in the parameters screen. For the body, we only want to change one parameter; the age of the person we study. As the simulation progress, the person will grow, so the we can only enter the initial age of the person.
The simulation screen lets you select what outputs (end-points or intermediary calculations) and for what time points you want data, what type of simulation you want to run etc.
The Information will keep you informed about simulation progress.
The charts screen and the tables screen lets you create plots and tables of simulation results. You can also export your results if you want to create proper plots/tables or perform post processing in another software such as Excel.
These two screens are very similar. After a simulation has been run, the available simulation outputs are listed on the left hand side, organised into folders. When you select an output which has values for different contaminants, types of food, etc., a panel appears that let you continue to select exactly which dependencies you want to plot. After, click one of the toolbar buttons to create different types of charts/tables.
A chart will now reveal the blood concentrations of the child.
The World Health Organisation lists the following effects for children that have been exposed to lead:
|Blood concentration (µg/L)||Effect|
|500-1000||Encephalopathy, Nephropathy, Frank anemia, Colic|
|250-500||Decreased hemoglobin synthesis, Increased vitamin D metabolism, increased risk of hypertension in adulthood|
|100-250||Increased nerve conduction velocity, increased level of erythrocyte protoporphyrin, decreased vitamin D metabolism, decreased calcium homeostasis|
To get the exact concentration a table is better.
A table with the blood concentrations should now appear. If you have Excel installed on your computer, you can view the data directly in Excel:
Otherwise, if you do not have Excel or if the above failed,
If you want to get a better understanding of the model you can generate a report. The report contain all equations and data that you have entered, the simulation settings and plots and tables you have created. Exactly what is displayed in the report can be fine tuned.