Pink Noise - Leonid Korogodski [59]
glial cells
Also known as glia, these are certain kinds of cells in the brain that provide support to neurons.
See also astrocyte.
Great Red Spot
An enormous plasma vortex on Jupiter, the Great Red Spot is an elongated oval at about 22° South, with slight but regular oscillations of its latitude. Its dimensions have varied widely over the centuries, from 40,000 × 14,000 km down to 10,000 × 3,000 km (the Earth’s diameter is 12,740 km), depending sensitively on the solar activity.
The Great Red Spot owes its name to the brick-red color that it possesses most often, although its color can change rapidly, on occasion totally disappearing from the visible range; when that happens, it looks like an enormous hole in the planet—or a sunspot.
H
hachure
An artistic technique where thinly spaced, short parallel lines are used in drawing to create the impression of a three-dimensional shape. The word hachure is French for “hatching,” another name for the technique. Cross-hatching uses similar lines crossing at an angle.
Hamiltonian potential
For a vector field, a Hamiltonian potential is a function whose value is constant along the field lines. In classical mechanics, it stands for the system’s energy. Its constancy is the energy conservation law. In quantum mechanics, the Hamiltonian is defined differently, as an operator. But it means the same—the system’s energy.
Hand of Evil
In the Dungeon Keeper series of games, the Hand of Evil is the cursor. One can use it to slap one’s minions, making them work harder, or on prisoners in torture chambers.
See also Dungeon Keeper.
Hellas Planitia
A huge depression in the southern hemisphere of Mars. Hellas Planitia is about 2,300 km wide, nearly the same as the length of the entire Himalaya chain of mountains on Earth. Hellas is 9 km deep, from rim to bottom, enough to cover the top of Everest. The rim is made of a circular chain of mountains, about 2 km tall. Hellas is home to some of the most exotic terrain in the solar system.
hemineglect
The author is a fan of the “singular they.”
A neurological condition caused by damage to certain parts of one hemisphere of the brain that makes it difficult or impossible for the patient to perceive the corresponding half of the perception field. In some cases, the patient doesn’t perceive anything on one side of their entire field of vision. In others, the patient can see only one side of every object.
The amazing thing about hemineglect is that it doesn’t feel as if anything is missing from the world. No matter what happens, consciousness always “closes” around the gaps, presenting an unbroken new model of the world, with the overwhelming sense of it being complete.
hippocampus
The brain’s search engine, the hippocampus works by bridging space and time. The so-called place cells in the hippocampus form a “map” of sorts, firing in the fashion that is dependent on the body’s current location. As we move, it’s like a solitary wave centered on its location moving across the “place map.”
The same place cells are responsible for navigating our memories. The episodic memories are linearly organized, along the arrow of time. But the semantic memory—of concepts rather than events—is based on “place maps” rather than paths. Building a map requires making trips down intersecting paths. In the same way, seeing one dog then another dog and so on eventually gives us the abstract idea of a “dog” in general. The concepts are like two-dimensional maps built from the intersecting paths of episodic memory.
honeycomb terrain
A rare kind of terrain found on Mars, in the deepest part of Hellas Planitia. The roughly oval and hexagonal depressions are separated by raised-lip walls with leaf-like patterns. The floor is often drawn with alternating light and dark bands.
I
idlozi,pl. amadlozi [Zulu]
Ancestor shade. In the traditionalist