Later, during the Koine Greek period, the aspirated and voiceless stops /tʰ d/ of Attic Greek lenited to voiceless and voiced fricatives, yielding /θ ð/ in Medieval and Modern Greek.
The lenited Attic Greek yielded /θ ð/ in what periods?
Medieval and Modern Greek

Lie groups are of fundamental importance in modern physics: Noether's theorem links continuous symmetries to conserved quantities. Rotation, as well as translations in space and time are basic symmetries of the laws of mechanics. They can, for instance, be used to construct simple models—imposing, say, axial symmetry on a situation will typically lead to significant simplification in the equations one needs to solve to provide a physical description.v[›] Another example are the Lorentz transformations, which relate measurements of time and velocity of two observers in motion relative to each other. They can be deduced in a purely group-theoretical way, by expressing the transformations as a rotational symmetry of Minkowski space. The latter serves—in the absence of significant gravitation—as a model of space time in special relativity. The full symmetry group of Minkowski space, i.e. including translations, is known as the Poincaré group. By the above, it plays a pivotal role in special relativity and, by implication, for quantum field theories. Symmetries that vary with location are central to the modern description of physical interactions with the help of gauge theory.
What connects continuous symmetries to conserved quantities?
Noether's theorem

Demand in Europe for Chinese goods such as silk, tea, and ceramics could only be met if European companies funneled their limited supplies of silver into China. In the late 1700s, the governments of Britain and France were deeply concerned about the imbalance of trade and the drain of silver. To meet the growing Chinese demand for opium, the British East India Company greatly expanded its production in Bengal. Since China's economy was essentially self-sufficient, the country had little need to import goods or raw materials from the Europeans, so the usual way of payment was through silver. The Daoguang Emperor, concerned both over the outflow of silver and the damage that opium smoking was causing to his subjects, ordered Lin Zexu to end the opium trade. Lin confiscated the stocks of opium without compensation in 1839, leading Britain to send a military expedition the following year.
What did the Chinese want in return?
silver