Where does spheroid collide?

In geodesy a spheroid is the slightly flattened sphere that approximates the shape of the rotating Earth. Newton argued in the Principia that because the Earth spins, centrifugal effect makes it bulge at the equator and flatten at the poles, so its figure is an oblate spheroid (an ellipsoid of revolution) rather than a true sphere, a prediction later confirmed by arc-measurement expeditions. The referent is the flattened-sphere figure of a rotating planet, characterised by how far the poles are flattened relative to the equator.[1]

Unit

Flattening: equatorial minus polar radius, over equatorial radius

Recovery means

Not applicable

Measured by

Determined from the difference between equatorial and polar radii and from the planet's gravity field

In cancer biology a spheroid is a roughly ball-shaped aggregate of cells grown in culture, used as a three-dimensional model of a small avascular tumour. Because oxygen and nutrients diffuse inward only from the surface, a spheroid develops concentric zones (a proliferating outer rim, a quiescent middle layer, and often a necrotic core) that reproduce the gradients of a real tumour microregion. Sutherland's multicell spheroid model established it as a workhorse of tumour and radiation biology. The referent is a 3-D cellular aggregate used to study the tumour microenvironment, sharing only its ball shape with a planet's figure.[2]

Unit

Spheroid diameter and the thickness of the viable cell rim

Recovery means

Not applicable

Measured by

Tracked by spheroid diameter over time and by oxygen and nutrient gradients across the aggregate