The vertebral region transmitting forces between the vertebral column and pelvic apparatus.

The posterior rod of the adult frog skeleton formed from Caudal vertebral and associated developmental components. It replaces a freely jointed adult tail and participates in force transmission.

The thickened medial portion of the cetacean auditory bulla, important in recognizing early whales before a fully aquatic skeleton evolved.

The atomic unit of energy, $E_h={\hslash }^2/(m_e{a}_0^2)$, approximately $27.2$ eV. The hydrogen-atom ground-state energy is $-E_h/2$.

A level of an atomic term with specified total angular momentum $J$. Without an external field, its $2J+1$ magnetic states remain degenerate in a rotationally invariant Hamiltonian.

A change of atomic-orbital basis used to construct directed local bonding orbitals. $sp$, $s{p}^2$ and $s{p}^3$ describe idealized combinations; they are model descriptions rather than unique experimental labels for every bonded atom.

An atomic orbital with orbital angular momentum quantum number $l=1$. Real $p_x,p_y,p_z$ combinations have opposite quantum phases in their two lobes and a nodal plane through the atomic nucleus. An orbital phase is not an electric charge.

A plane on which an atomic orbital wavefunction vanishes. For a real p orbital oriented along $x$, it is the plane $x=0$. The probability density also vanishes on that plane.

An atomic orbital with orbital angular momentum quantum number $l=2$. Five angular functions span the subshell; a ligand field can split their energies.

An atomic orbital with orbital angular momentum quantum number zero. Its angular part is spherically symmetric; higher principal shells can have radial nodes.

A radial position at which an orbital radial wavefunction vanishes. A hydrogen-like orbital has $n-l-1$ radial nodes; $2s$ has one and $2p$ none.

An atomic nucleus with odd proton number and odd neutron number. Both unpaired species can contribute to the total nuclear spin; addition of angular momentum gives possible couplings, while the nuclear residual interaction determines their ordering.

A nuclear excited state lies above the same nucleus's ground state in internal energy. spin, parity and approximate isospin help classify it. Single-particle rearrangements, broken pairs and collective deformation/vibration give different excitation patterns and can mix. Below particle-emission thresholds, gamma decay and internal conversion are important de-excitation routes; an excitation energy is not necessarily the energy of every emitted gamma ray in a cascade.

An atomic force microscope measures interactions through the deflection or dynamics of a calibrated compliant cantilever. In a static force curve, calibrated deflection $d$ and spring constant $k_c$ give $F=k_{c}d$; converting stage position to a surface gap also requires the bending correction and a contact reference. The colloidal probe technique replaces a sharp probe with a sphere of controlled radius.

Attach a sphere to an atomic force microscope cantilever and approach a planar surface in a controlled fluid. Calibrated cantilever bending measures force as a function of corrected surface separation. The sphere's known curvature allows comparison with planar interaction models through the Derjaguin approximation. Approach speed, charge, roughness, hydration and jump-to-contact can limit interpretation.

A 1991 demonstration used a $3.5\mu \mathrm{m}$ radius silica sphere against a plane in sodium chloride solutions. The reported double-layer agreement and short-range deviations illustrate both the method and the need to distinguish electrostatic forces from a presumed purely dispersive interaction.^[ref]

An oscillatory probe mode in which a controller uses changes in the cantilever amplitude to adjust probe-surface separation. The recorded topography depends on both tip geometry and tracking dynamics.