Moreover, as already discussed above, the component entities of any aggregate of material entities can be spatially separated.
If we want to refer to an aggregate of material entities that forms a cohesive/connected whole consisting of several material entities we are referring to a cluster.
This possible constellation holds for any aggregate of material entities: every aggregate of material entities can possess immaterial parts (i.e. negative objects: certain types of holes, e.g., tunnels, caves, tubes and hollows), which are continuously connected to the space surrounding the aggregate.
Any type of aggregate of material entities, be it a group or a cluster, cannot be an object: groups of material entities are not objects, because their material entity parts are separated from each other by spatial gaps (Fig. 4).
Definition: A cluster is an aggregate of material entities that is a mereological sum of separate material entities, which adhere to one another through chemical bonds or physical junctions that go beyond gravity.
For example, whenever we want to refer to an aggregate of material entities that exhibits a specific spatial distribution pattern of scattered material entities we are referring to a group.
The distinction between groups and clusters requires to further differentiate the three basic types of aggregate of material entities discussed so far, i.e. object aggregate, fiat object part aggregate, and object with fiat object part aggregate, into respective types of clusters and groups (table 2; Fig. 6).
Definition: A group is an aggregate of material entities that is a mereological sum of spatially separated material entities, which do not adhere to one another through chemical bonds or physical junctions but, instead, relate to one another merely on grounds of metric proximity.
A literature survey of the subject found that a clear knowledge gap exists in this area of study, only aggregate data of materials of ships is available, no ship by ship data exist.
They appear to be primarily aggregates of material that formed in the solar nebula prior to or during planet formation.
For exposures greater than 3 minutes, it was difficult to find any bacteria on the washers, and only scattered aggregates of material were visible on the washer surface.
