Glossary
- Page ID
- 419697
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| (Eg. "Genetic, Hereditary, DNA ...") | (Eg. "Relating to genes or heredity") |  |
The infamous double helix | https://bio.libretexts.org/ | CC-BY-SA; Delmar Larsen |
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Word(s) |
Definition |
Image | Caption | Link | Source |
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| Canonical transformation | A transformation in which the phase space variables Q and P are transformed to new phase space variables q and p but the canonical equations of motion (Hamilton’s) are preserved. | ||||
| Coupling |
An interaction between particles, fields, or quantum states. Typically refers to a term in a Hamiltonian that describes the influence of one particle or molecular quantity on another. Potential couplings describe the potential energy as a function of the time-dependent position of two or more particles or fields, whereas kinetic couplings depend on their momenta. Coupling is also used to refers to off-diagonal terms or matrix elements in a matrix Hamiltonian. Coupling to an external potential, for instance in perturbation theory, typically only accounts for the influence of the external interactions on the system of interest rather that the mutual effect of two particles on each other. |
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| Damping | The time-dependent decrease in the amplitude of an oscillating system due to dissipation, friction, or a viscous force. | ||||
| Degrees of freedom |
Independent variables describing the position and momenta of particles. While a particle is described by six canonical variables, i.e. the \(x,y,z\) components of the position and momentum at a certain time point, we refer to this as three degrees of freedom or a three dimensional problem. |
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| Dissipation | The irreversible flow of energy out of a system into its surroundings. This typically refers to the flow of energy in the form of heat, and can be used in the context of an equilibrium, steady-state or non-equilibrium process. | ||||
| Exciton | An electron-hole pair that results from electronic excitation. | ||||
| Field | A physical quantity that is assigned to a position in space. A field can be static or time-dependent. It can be a scalar field with only one value at each point or it can be a vector field which assigns a vector to each point. An example of a time-dependent vector field is velocity. | ||||
| FWHM | Stands for Full Width at Half Maximum. This is the standard general metric for the width of a lineshape. The frequency width is measured between the 50% amplitude points between the peak and baseline. For a Gaussian lineshape the FWHM \(=2.35\sigma\). | ||||
| Gauge transformation |
A transformation of the vector and scalar electromagnetic potentials that leaves the observable electric and magnetic fields unchanged. See Section 7.8. |
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| Polaron | Electronic excitation of a lattice in which the atoms around the excitation are polarized, and the deformation propagates in time. A large polaron is one in which the polarization is over a region much larger than the lattice spacing, whereas a small polaron extends over a region approximately equal to the lattice spacing. | ||||
| Quasiparticle | Delocalized quantum excitations spanning many particles whose behavior can be described like a single particle: photons, phonons, excitons, plasmons, holes. | ||||
| Relaxation |
The return of population in a non-equilibrium system to its equilibrium distribution. |
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| Unitary transformation |
A transformation that results in a different representation of the wavefunction, but the state of the system is unchanged. |