head

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head

1. the upper or front part of the body in vertebrates, including man, that contains and protects the brain, eyes, mouth, and nose and ears when present
2. the corresponding part of an invertebrate animal
3. the froth on the top of a glass of beer
4. Botany
a. a dense inflorescence such as that of the daisy and other composite plants
b. any other compact terminal part of a plant, such as the leaves of a cabbage or lettuce
5. the pus-filled tip or central part of a pimple, boil, etc.
6. the source or origin of a river or stream
7. a headland or promontory, esp a high one
8. the obverse of a coin, usually bearing a portrait of the head or a full figure of a monarch, deity, etc.
9. Nautical
a. the front part of a ship or boat
b. (in sailing ships) the upper corner or edge of a sail
c. the top of any spar or derrick
d. any vertical timber cut to shape
10. the taut membrane of a drum, tambourine, etc.
11. 
a. the height of the surface of liquid above a specific point, esp when considered or used as a measure of the pressure at that point
b. pressure of water, caused by height or velocity, measured in terms of a vertical column of water
c. any pressure
12. Slang
a. a person who regularly takes drugs, esp LSD or cannabis
b. (in combination): an acid head
13. a device on a turning or boring machine, such as a lathe, that is equipped with one or more cutting tools held to the work by this device
14. See cylinder head
15. an electromagnet that can read, write, or erase information on a magnetic medium such as a magnetic tape, disk, or drum, used in computers, tape recorders, etc.
16. Informal short for headmaster, headmistress
17. 
a. the head of a horse considered as a narrow margin in the outcome of a race (in the phrase win by a head)
b. any narrow margin of victory (in the phrase (win) by a head)
18. Informal short for headache
19. Curling the stones lying in the house after all 16 have been played
20. Bowls the jack and the bowls that have been played considered together as a target area
21. against the head Rugby from the opposing side's put-in to the scrum

Head

Edith. 1907--81, US dress designer: won many Oscars for her Hollywood film costume designs

head

The coma and nucleus of a comet when seen together. In this context ‘nucleus' means the diffuse starlike luminous condensation sometimes observed in the coma. The head generally contracts as perihelion is approached and expands again afterward. Remarkable changes in size, luminosity distribution, and the number of observed ‘nuclei’ can take place inside the head in a few hours.

Head

In general, the uppermost member of any structure. The upper horizontal cross-member between jambs, which forms the top of a door or window frame; may provide structural support for construction above.

Head

 

the anterior (or superior, in humans particularly) section of the body (separate from the trunk) of motile bilaterally symmetrical animals.

The upper division of the central nervous system, some sense organs, and the anterior sections of the digestive and respiratory systems are concentrated in the head. The anterior end of an animal, as yet undifferentiated but already structurally distinguishable from the rest of the body (for example, in the majority of worms) is called the cephalic end. The head, which is well-differentiated in some mollusks and especially in arthropods, became distinct from the cephalic end through the course of further evolution. Among the chor-dates, a differentiated head is present in the vertebrates (in connection with the progressive development of the central nervous system). Concentrated in the head of vertebrates are the brain, enclosed in the skull, the organs of smell, sight, and hearing; the organs of the oral and pharyngeal cavities, surrounded by the visceral arch; and, in lower vertebrates, the organs of the lateral line. In cyclostomes and the majority of fish the head is immovably attached to the spine. In terrestrial vertebrates the head is movable because of the separation of the cervical section of the body and the development of movable articulation of the skull with the spine. In amniotes (reptiles, birds, and mammals), with the formation of a clearly defined cervical section, the head is noticeably set apart from the torso (except in secondarily aquatic forms—that is, cetaceans and, among fossils, ichthyosaurs). In addition to mobility in the atlantooccipital joint, the head in amniotes may rotate together with the atlas around the dens axis, or epistropheus. The most mobile is the head of birds and the majority of mammals; this is associated with the progressive evolution of higher nervous activity and of the sense organs-olfactory, visual, and auditory.

Head development, which is of great importance in the evolution of vertebrates, is called cerebralization. In man, the head has anatomic features that are determined by the high level of brain development, the vertical position of the body, the transition to bipedalism, and the conversion of the hands to organs of work.

A. N. DRUZHININ


Head

 

(in hydraulics), a linear quantity expressing the specific energy (per unit weight) of a liquid stream at a particular point.

The total reserve of specific energy H of a stream (the total head) is defined by Bernoulli’s equation: H = z + (pv/γ) + (v2/2g), where z is the height of the point above the reference plane, pv, is the pressure of the liquid flowing with velocity v,γ is the density of the liquid, and g is the acceleration of gravity. The sum of the first two terms of the trinomial represents the sum of the specific potential energies of position (z) and pressure (pv/γ)—that is, the total content of specific potential energy, or the hydrostatic head. The third term represents the specific kinetic energy (the velocity head). The head decreases in the direction of flow. The difference between the heads in two cross sections of a real liquid H1 —H2 = hv is called the loss of head or lost head. For the motion of a viscous liquid in pipes the loss of head is determined by Darcy’s formula.

In the design of hydroengineering structures the head assumed in calculations is chosen in accordance with a given task. For example, for dams the head of the headrace is the depth of water in the headrace. In problems dealing with the flow of liquids or gases from orifices, the head is assumed to be the immersion depth of the “center of gravity” of the opening (for outflow of liquid) or the pressure differential (for outflow of gas). In hydroelectric power plants a distinction is made between the gross head (the difference between the elevations of the headrace and tailwater) and the net head (the gross head less the loss of head caused by hydraulic resistance).

REFERENCES

Chugaev, R. R. Gidravlika, 2nd ed. Moscow, 1971.
Spravochnik po gidravlicheskim raschetam, 4th ed. Edited by P. G. Kiselev. Moscow-Leningrad, 1972.

P. G. KISELEV

What does it mean when you dream about your head?

The head symbolizes the source of all wisdom. Being made the “head” of an organization, or being sent to the “head of the class” denotes that one has accomplished much.

head

[hed]
(anatomy)
The region of the body consisting of the skull, its contents, and related structures.
Proximal end of a long bone.
(astronomy)
(botany)
A dense cluster of nearly sessile flowers on a very short stem.
(building construction)
The upper part of the frame on a door or window.
(computer science)
A device that reads, records, or erases data on a storage medium such as a drum or tape; examples are a small electromagnet or a sensing or punching device.
(electronics)
The photoelectric unit that converts the sound track on motion picture film into corresponding audio signals in a motion picture projector.
(engineering)
The end section of a plastics blow-molding machine in which a hollow parison is formed from the melt.
The section of a shell-and-tube heat exchanger from which fluid from the tube bundle is discharged.
(engineering acoustics)
(fluid mechanics)
(geography)

head

1. In general, the top or upper member of any structure; the top or end (esp. the more prominent end) of a piece or member.
2. The upper horizontal cross member, between the jambs, which forms the top of a door or window frame; may provide structural support for construction above if required, as a doorhead or window head.
3. A stone that has one end dressed to match the face because the end will be exposed at a corner or in a reveal.
4. A roofing tile of half the usual length but of the same width; for forming the first course at the eaves.

head

head
Hingeless rotor head.
As it pertains to helicopters, the complete hub of the helicopter rotor—both main and tail—including flight control linkages and all auxiliaries' connections.