I searched for the title of that article, and found it had been published elsewhere, e.g. https://pe2bz.philpem.me.uk/Detect-Sense/-%20Air-Gas/T-101-DiffHeat-senceAirFlow/DisplayDocument.pdf
Here is Figure 1 from the above; see references below to earlier articles.
The circuit in Figure 1 combines
ideas from two earlier IFDs (“Low-
Power Thermal Airspeed Sensor,”
ELECTRONIC DESIGN, May 25, 1998, p. 116;
and “Low-Power Solid-State Airflow Detector,”
ELECTRONIC DESIGN, Jan. 22, 2001, p.
118).