The phrase "are activated when a" is correct and usable in written English.
It can be used in contexts where you are describing a condition or event that triggers an activation process.
Example: "The safety features are activated when a certain threshold is exceeded."
Alternatives: "are triggered when a" or "become active when a".
The scans suggest that particular circuits in the brain are activated when a mother distinguishes the smiles and cries of her own baby from those of other infants.
Receptors are activated when a high-affinity ligand receptor complex is generated.
This theory argues that similar parts of the brain are activated when a human makes a movement as when an external agent makes the same movement [7, 22].
Immune system cells are activated when a small signaling ligand binds to a receptor within the cells, but the ligand is only weakly attracted.
The intrusion prevention and detection system are activated when a person or a large object is in the track area, and the immediate emergency braking could be initiated depending on how far away the approaching train is.
Functional Magnetic Resonance Imaging (fMRI) research has shown that specific brain regions are activated when a person engages in cognitive flexibility tasks.
Recent experiments have shown that 'mirror' neurons are activated when an action is being performed, perceived, or verbally referred to.
The Rules are activated when an event occurs in the Knowledge Base for example when a new call is added.
Senor node then changes its state from sleep to active state 3. SN_S This is activated when a node finishes sending/receiving data or self timer expires.
Cambia is trying to mimic the natural process by inserting a packet of DNA from yeast, bacteria and corn DNA that can only be activated when a rice gene is nearby and active.
On the one hand, they consider that all genes in a gene set or a pathway equally contribute to the activity of that pathway; hence, the pathway is activated when a "sufficient" number of gene members is activated.
