Question: What developer of the Bragg–Gray cavity theory was knighted in 1920?

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Flammulated flycatcher: The flammulated flycatcher ("Deltarhynchus flammulatus") is a species of bird in the family Tyrannidae and is the only species in the monotypic genus Deltarhynchus, although it is closely related to the birds of the genus "Myiarchus".  It is endemic to the dry deciduous forest, arid thorn forest, and scrubby woodland of Mexico’s Pacific coast.  The flycatcher is an olive to gray-brown bird with a streaked, pale gray chest, white throat, black bill, dark gray feet, and dark brown wings.  It is a skulking bird that typically remains hidden in the underbrush.  It feeds by gleaning insects off of leaves and twigs that it spots from an exposed perch.  The female lays approximately three eggs in a nest made in a shallow tree cavity.

Cavity optomechanics: Cavity optomechanics is a branch of physics which focuses on the interaction between light and mechanical objects on low-energy scales.  It is a cross field of optics, quantum optics, solid-state physics and materials science.  The motivation for research on cavity optomechanics comes from fundamental effects of quantum theory and gravity, as well as technological applications.

Distributed Bragg reflector laser: A distributed Bragg reflector laser (DBR) is a type of single frequency laser diode.  Other practical types of single frequency laser diodes include DFB lasers and external cavity diode lasers.  A fourth type, the cleaved-coupled-cavity laser has not proven to be commercially viable.  VCSELs are also single frequency devices.

Reaction field method: The reaction field method is used in molecular simulations to simulate the effect of long range dipole-dipole interactions for simulations with periodic boundary conditions.  Around each molecule there is a 'cavity' or sphere within which the Coulomb interactions are treated explicitly.  Outside of this cavity the medium is assumed to have a uniform dielectric constant.  The molecule induces polarization in this media which in turn creates a reaction field, sometimes called the Onsager reaction field.  Although Onsager's name is often attached to the technique, because he considered such a geometry in his theory of the dielectric constant, the method was first introduced by Barker and Watts in 1973.

Bragg–Gray cavity theory: According to the Bragg–Gray cavity theory, the ionization produced in a small cavity within an irradiated medium or object is related to the energy absorbed in that medium as a result of its radiation exposure.  It was developed in 1936 by British scientists Louis Harold Gray, William Henry Bragg, and William Lawrence Bragg.

Dielectric mirror: A dielectric mirror, also known as a Bragg mirror, is a type of mirror composed of multiple thin layers of dielectric material, typically deposited on a substrate of glass or some other optical material.  By careful choice of the type and thickness of the dielectric layers, one can design an optical coating with specified reflectivity at different wavelengths of light.  Dielectric mirrors are also used to produce ultra-high reflectivity mirrors: values of 99.999% or better over a narrow range of wavelengths can be produced using special techniques.  Alternatively, they can be made to reflect a broad spectrum of light, such as the entire visible range or the spectrum of the Ti-sapphire laser.  Mirrors of this type are very common in optics experiments, due to improved techniques that allow inexpensive manufacture of high-quality mirrors.  Examples of their applications include laser cavity end mirrors, hot and cold mirrors, thin-film beamsplitters, and the coatings on modern mirrorshades.

Jubie Bragg: Jubie Barton Bragg (February 17, 1876 – November 26, 1947) was an American football coach.  He served the first head football coach at Florida A&M University in Tallahassee, Florida.  Bragg coached the team off and on from 1907 through 1931 and has also served as head coach of Alabama's Talladega College, leading that school to shared black college football national championships in 1920 and 1921.  Bragg compiled a record of 4–18–1 as Florida A&M's head coach.  His son, Eugene J. Bragg, later coached the team himself.  Bragg was a member of Alpha Phi Alpha fraternity and a charter member of Alpha's Beta Nu chapter on the campus of Florida A&M.

Oscar Hertwig: Oscar Hertwig (21 April 1849 in Friedberg – 25 October 1922 in Berlin) was a German zoologist and professor, who also wrote about the theory of evolution circa 1916, over 55 years after Charles Darwin's book "The Origin of Species".  He was the elder brother of zoologist-professor Richard Hertwig (1850–1937). The Hertwig brothers were the most eminent scholars of Ernst Haeckel (and Carl Gegenbaur) from the University of Jena.  They were independent of Haeckel's philosophical speculations but took his ideas in a positive way to widen their concepts in zoology.  Initially, between 1879–1883, they performed embryological studies, especially on the theory of the coelom (1881), the fluid-filled body cavity.  These problems were based on the phylogenetic theorems of Haeckel, i.e. the biogenic theory (German = biogenetisches Grundgesetz), and the "gastraea theory".

Franz Xaver Rudolf von Höhnel: Franz Xaver Rudolf von Höhnel (24 September 1852 – 11 November 1920) was an Austrian bryologist, mycologist, and algologist, brother of explorer Ludwig von Höhnel (1857–1942).  He obtained his PhD in Strasbourg in 1877, and was a professor of botany in the Vienna University of Technology from 1884 to 1920.  Höhnel described roughly 250 new genera and 500 species of fungi, and was known for his contributions to the taxonomy of the Coelomycetes (asexual fungi that form conidia in a cavity (pycnidia) or a mat-like cushion of hyphae).  He died in Vienna on November 11, 1920.

William Henry Bragg: Sir William Henry Bragg (2 July 1862 – 12 March 1942) was a British physicist, chemist, mathematician and active sportsman who uniquely shared a Nobel Prize with his son William Lawrence Bragg – the 1915 Nobel Prize in Physics: ""for their services in the analysis of crystal structure by means of X-rays"".  The mineral Braggite is named after him and his son.  He was knighted in 1920.

Supporting paragraphs: Bragg–Gray cavity theory William Henry Bragg
Answer: William Henry Bragg