hemispherical-30

求关于蘑菇的英文介绍

An inertial navigation system is a navigation aid that uses a computer and motion sensors to continuously track the position, orientation, and velocity (direction and speed of movement) of a vehicle without the need for external references. Other terms used to refer to inertial navigation systems or closely related devices include inertial guidance system, inertial reference platform, and many other variations.。

Overview

An inertial navigation system includes at least a computer and a platform or module containing accelerometers, gyroscopes, or other motion-sensing devices. The INS is initially provided with its position and velocity from another source (a human operator, a GPS satellite receiver, etc.), and thereafter computes its own updated position and velocity by integrating information received from the motion sensors. The advantage of an INS is that it requires no external references in order to determine its position, orientation, or velocity once it has been initialized.。

An INS can detect a change in its geographic position (a move east or north, for example), a change in its velocity (speed and direction of movement), and a change in its orientation (rotation about an axis). It does this by measuring the linear and angular accelerations applied to the system. Since it requires no external reference (after initialization), it is immune to jamming and deception.。

Inertial-navigation systems are used in many different types of vehicles, including aircraft, submarines, spacecraft, and guided missiles. However, their cost and complexity does place constraints on the environments in which they are practical for use.。

Gyroscopes measure the angular velocity of the system in the inertial reference frame. By using the original orientation of the system in the inertial reference frame as the initial condition and integrating the angular velocity, the system's current orientation is known at all times. This can be thought of as the ability of a blindfolded passenger in a car to feel the car turn left and right or tilt up and down as the car ascends or descends hills. Based on this information alone, he knows what direction the car is facing but not how fast or slow it is moving, or whether it is sliding sideways.。

Accelerometers measure the linear acceleration of the system in the inertial reference frame, but in directions that can only be measured relative to the moving system (since the accelerometers are fixed to the system and rotate with the system, but are not aware of their own orientation). This can be thought of as the ability of a blindfolded passenger in a car to feel himself pressed back into his seat as the vehicle accelerates forward or pulled forward as it slows down; and feel himself pressed down into his seat as the vehicle accelerates up a hill or rise up out of his seat as the car passes over the crest of a hill and begins to descend. Based on this information alone, he knows how the vehicle is moving relative to itself, that is, whether it is going forward, backward, left, right, up (toward the car's ceiling), or down (toward the car's floor) measured relative to the car, but not the direction relative to the Earth, since he did not know what direction the car was facing relative to the Earth when he felt the accelerations.。

However, by tracking both the current angular velocity of the system and the current linear acceleration of the system measured relative to the moving system, it is possible to determine the linear acceleration of the system in the inertial reference frame. Performing integration on the inertial accelerations (using the original velocity as the initial conditions) using the correct kinematic equations yields the inertial velocities of the system, and integration again (using the original position as the initial condition) yields the inertial position. In our example, if the blindfolded passenger knew how the car was pointed and what its velocity was before he was blindfolded, and he is able to keep track of both how the car has turned and how it has accelerated and decelerated since, he can accurately know the current orientation, position, and velocity of the car at any time.。

All inertial navigation systems suffer from integration drift: Small errors in the measurement of acceleration and angular velocity are integrated into progressively larger errors in velocity, which is compounded into still greater errors in position. This is a problem that is inherent in every open loop control system. The inaccuracy of a good-quality navigational system is normally fewer than 0.6 nautical miles per hour in position and on the order of tenths of a degree per hour in orientation.。

Inertial navigation may also be used to supplement other navigation systems, providing a higher degree of accuracy than is possible with the use of any single navigation system. For example, if, in terrestrial use, the inertially tracked velocity is intermittently updated to zero by stopping, the position will remain precise for a much longer time, a so-called zero velocity update.。

Control theory in general and Kalman filtering in particular provide a theoretical framework for combining information from various sensors. One of the most common alternative sensors is a satellite navigation radio, such as GPS. By properly combining the information from an INS and the GPS system, the errors in position and velocity are stable GPS/INS.。

[edit] History

Inertial navigation systems were originally developed for rockets. American rocket pioneer Robert Goddard experimented with rudimentary gyroscopic systems. Dr. Goddard's systems were of great interest to contemporary German pioneers including Wernher von Braun. The systems entered more widespread use with the advent of spacecraft, guided missiles, and commercial airliners.。

One example of a popular INS for commercial aircraft was the Delco Carousel, which provided partial automation of navigation in the days before complete flight management systems became commonplace. The Carousel allowed pilots to enter a series of waypoints, and then guided the aircraft from one waypoint to the next using an INS to determine aircraft position. Some aircraft were equipped with dual Carousels for safety.。

[edit] Inertial navigation systems in detail。

INSs have angular and linear accelerometers (for changes in position); some include a gyroscopic element (for maintaining an absolute angular reference).。

Angular accelerometers measure how the vehicle is rotating in space. Generally, there's at least one sensor for each of the three axes: pitch (nose up and down), yaw (nose left and right) and roll (clockwise or counter-clockwise from the cockpit).。

Linear accelerometers measure how the vehicle is moving in space. Since it can move in three axes (up & down, left & right, forward & back), there is a linear accelerometer for each axis.。

A computer continually calculates the vehicle's current position. First, for each of the six degrees of freedom (x,y,z and θ x, θ y and θ z), it integrates the sensed amount of acceleration over time to figure the current velocity. Then it integrates the velocity to figure the current position.。

Inertial guidance is difficult without computers. The desire to use inertial guidance in the Minuteman missile and Project Apollo drove early attempts to miniaturize computers.。

Inertial guidance systems are now usually combined with satellite navigation systems through a digital filtering system. The inertial system provides short term data, while the satellite system corrects accumulated errors of the inertial system.。

An inertial guidance system that will operate near the surface of the earth must incorporate Schuler tuning so that its platform will continue pointing towards the center of the earth as a vehicle moves from place to place.。

[edit] Basic schemes。

[edit] Gimballed gyrostabilized platforms。

Some systems place the linear accelerometers on a gimbaled gyrostabilized platform. The gimbals are a set of three rings, each with a pair of bearings initially at right angles. They let the platform twist about any rotational axis (or, rather, they let the platform keep the same orientation while the vehicle rotates around it). There are two gyroscopes (usually) on the platform.。

Two gyroscopes are used to cancel gyroscopic precession, the tendency of a gyroscope to twist at right angles to an input force. By mounting a pair of gyroscopes (of the same rotational inertia and spinning at the same speed) at right angles the precessions are cancelled, and the platform will resist twisting.。

This system allows a vehicle's roll, pitch, and yaw angles to be measured directly at the bearings of the gimbals. Relatively simple electronic circuits can be used to add up the linear accelerations, because the directions of the linear accelerometers do not change.。

The big disadvantage of this scheme is that it uses many expensive precision mechanical parts. It also has moving parts that can wear out or jam, and is vulnerable to gimbal lock. The primary guidance system of the Apollo spacecraft used a three-axis gyrostabilized platform, feeding data to the Apollo Guidance Computer. Maneuvers had to be carefully planned to avoid gimbal lock.。

[edit] Fluid-suspended gyrostabilized platforms。

Gimbal lock constrains maneuvring, and it would be beneficial to eliminate the slip rings and bearings of the gimbals. Therefore, some systems use fluid bearings or a flotation chamber to mount a gyrostabilized platform. These systems can have very high precisions (e.g. Advanced Inertial Reference Sphere). Like all gyrostabilized platforms, this system runs well with relatively slow, low-power computers.。

The fluid bearings are pads with holes through which pressurized inert gas (such as Helium) or oil press against the spherical shell of the platform. The fluid bearings are very slippery, and the spherical platform can turn freely. There are usually four bearing pads, mounted in a tetrahedral arrangement to support the platform.。

In premium systems, the angular sensors are usually specialized transformer coils made in a strip on a flexible printed circuit board. Several coil strips are mounted on great circles around the spherical shell of the gyrostabilized platform. Electronics outside the platform uses similar strip-shaped transformers to read the varying magnetic fields produced by the transformers wrapped around the spherical platform. Whenever a magnetic field changes shape, or moves, it will cut the wires of the coils on the external transformer strips. The cutting generates an electric current in the external strip-shaped coils, and electronics can measure that current to derive angles.。

Cheap systems sometimes use bar codes to sense orientations, and use solar cells or a single transformer to power the platform. Some small missiles have powered the platform with light from a window or optic fibers to the motor. A research topic is to suspend the platform with pressure from exhaust gases. Data is returned to the outside world via the transformers, or sometimes LEDs communicating with external photodiodes.。

[edit] Strapdown systems。

Lightweight digital computers permit the system to eliminate the gimbals, creating "strapdown" systems, so called because their sensors are simply strapped to the vehicle. This reduces the cost, eliminates gimbal lock, removes the need for some calibrations, and increases the reliability by eliminating some of the moving parts. Angular rate sensors called "rate gyros" measure how the angular velocity of the vehicle changes.。

A strapdown system has a dynamic measurement range several hundred times that required by a gimbaled system. That is, it must integrate the vehicle's attitude changes in pitch, roll and yaw, as well as gross movements. Gimballed systems could usually do well with update rates of 50 to 60 updates per second. However, strapdown systems normally update about 2000 times per second. The higher rate is needed to keep the maximum angular measurement within a practical range for real rate gyros: about 4 milliradians. Most rate gyros are now laser interferometers.。

The data updating algorithms ("direction cosines" or "quaternions") involved are too complex to be accurately performed except by digital electronics. However, digital computers are now so inexpensive and fast that rate gyro systems can now be practically used and mass-produced. The Apollo lunar module used a strapdown system in its backup Abort Guidance System (AGS).。

Strapdown systems are nowadays commonly used in commercial and tactical applications (arcraft, missiles, etc). However they are still not widespread in applications where superb accuracy is required (like submarine navigation or strategic ICBM guidance).。

[edit] Motion-based alignment。

The orientation of a gyroscope system can sometimes also be inferred simply from its position history (e.g., GPS). This is, in particular, the case with planes and cars, where the velocity vector usually implies the orientation of the vehicle body.。

For example, Honeywell's Align in Motion[1] is an initialization process where the initialization occurs while the aircraft is moving, in the air or on the ground. This is accomplished using GPS and an inertial reasonableness test, thereby allowing commercial data integrity requirements to be met. This process has been FAA certified to recover pure INS performance equivalent to stationary align procedures for civilian flight times up to 18 hours. It avoids the need for gyroscope batteries on aircraft.。

[edit] Vibrating gyros。

Less-expensive navigation systems, intended for use in automobiles, may use a Vibrating structure gyroscope to detect changes in heading, and the odometer pickup to measure distance covered along the vehicle's track. This type of system is much less accurate than a higher-end INS, but it is adequate for the typical automobile application where GPS is the primary navigation system, and dead reckoning is only needed to fill gaps in GPS coverage when buildings or terrain block the satellite signals.。

[edit] Hemispherical Resonator Gyros ("Brandy Snifter Gyros")。

If a standing wave is induced in a globular resonant cavity (i.e. a brandy snifter), and then the snifter is tilted, the waves tend to continue oscillating in the same plane of movement - they don't fully tilt with the snifter. This trick is used to measure angles. Instead of brandy snifters, the system uses hollow globes machined from piezoelectric materials such as quartz. The electrodes to start and sense the waves are evaporated directly onto the quartz.。

This system has almost no moving parts, and is very accurate. However it is still relatively expensive due to the cost of the precision ground and polished hollow quartz spheres.。

Although successful systems were constructed, and an HRG's kinematics appear capable of greater accuracy, they never really caught on. Laser gyros were just more popular.。

The classic system is the Delco 130Y Hemispherical Resonator Gyro, developed about 1986. See also [1] for a picture of an HRG resonator.。

[edit] Quartz rate sensors。

This system is usually integrated on a silicon chip. It has two mass-balanced quartz tuning forks, arranged "handle-to-handle" so forces cancel. Aluminum electrodes evaporated onto the forks and the underlying chip both drive and sense the motion. The system is both manufacturable and inexpensive. Since quartz is dimensionally stable, the system can be accurate.。

As the forks are twisted about the axis of the handle, the vibration of the tines tends to continue in the same plane of motion. This motion has to be resisted by electrostatic forces from the electrodes under the tines. By measuring the difference in capacitance between the two tines of a fork, the system can determine the rate of angular motion.。

Current state of the art non-military technology (2005) can build small solid state sensors that can measure human body movements. These devices have no moving parts, and weigh about 50 grams.。

Solid state devices using the same physical principles are used to stabilize images taken with small cameras or camcorders. These can be extremely small (≈5 mm) and are built with MEMS (Microelectromechanical Systems) technologies.。

[edit] MHD sensor。

Sensors based on magnetohydrodynamic principles can be used to measure angular velocities and are described in "MHD sensor".。

[edit] Laser gyros。

Laser gyroscopes were supposed to eliminate the bearings in the gyroscopes, and thus the last bastion of precision machining and moving parts.。

A laser gyro splits a beam of laser light into two beams in opposite directions through narrow tunnels in a closed optical circular path around the perimeter of a triangular block of temperature stable cervit glass block with reflecting mirrors placed in each corner. When the gyro is rotating at some angular rate, the distance traveled by each beam becomes different - the shorter path being opposite to the rotation. The phase-shift between the two beams can be measured by an interferometer, and is proportional to the rate of rotation (Sagnac effect).。

In practice, at low rotation rates the output frequency can drop to zero after the result of "Back scattering" causing the beams to synchronise and lock together. This is known as a "lock-in, or laser-lock." The result is that there is no change in the interference pattern, and therefore no measurement change.。

To unlock the counter-rotating light beams, laser gyros either have independent light paths for the two directions (usually in fiber optic gyros), or the laser gyro is mounted on a piezo-electric dither motor that rapidly vibrates the laser ring back and forth about its input axis through the lock-in region to decouple the light waves.。

The shaker is the most accurate, because both light beams use exactly the same path. Thus laser gyros retain moving parts, but they do not move as far.。

[edit] Pendular accelerometers。

Principle of open loop accelerometer. Acceleration in the upward direction causes the mass to deflect downward.The basic, open-loop accelerometer consists of a mass attached to a spring. The mass is constrained to move only in-line with the spring. Acceleration causes deflection of the mass and the offset distance is measured. The acceleration is derived from the values of deflection distance, mass, and the spring constant. The system must also be damped to avoid oscillation. A closed-loop accelerometer achieves higher performance by using a feedback loop to cancel the deflection, thus keeping the mass nearly stationary. Whenever the mass deflects, the feedback loop causes an electric coil to apply an equally negative force on the mass, cancelling the motion. Acceleration is derived from the amount of negative force applied. Because the mass barely moves, the non-linearities of the spring and damping system are greatly reduced. In addition, this accelerometer provides for increased bandwidth past the natural frequency of the sensing element.。

Both types of accelerometers have been manufactured as integrated micromachinery on silicon chips.。

求关于蘑菇的英文介绍

Usually known as the mushroom fungus is in a class, that is, the fruiting bodies of fungi burden. The burden is the fruiting bodies of fungi growing on the ground floor, looks very much like to play in the Village of an umbrella. On the ground floor there is albicans filamentous, spread all over the mycelium, which is the burden of nutrition-related bacteria, that is, non-reproductive organs. To a certain temperature and humidity conditions, to obtain mycelial enough nutrients on the fruit began to take shape. In the early fruiting body as eggs exposed on the ground, rapidly developed into a fruiting body, Jungai, stipe, up bacteria, fungi such as the ring. Mature fruit body shape, size, height, color, texture, and so very different. The large-diameter up to about 40 cm high up to about 50 cm; little less than half centimeters in diameter, 1 cm high, however. It will now be part of the description of the characters are as follows: Jungai fruiting body is the most obvious, like a hat. Wide variety of shapes, there are common bell-shaped, hats shaped, hemispherical, flat-shaped, funnel-shaped, and so on. Jungai color complex, although basically can identify white, yellow, brown, gray, red, green, purple color, and so on, but there are all kinds of deep color, light, light, strong differences are more common Mixed color. Young and old when they cooked the color can be different from the edge of the central government and the color is often the difference. Surface dry, wet, sticky, smooth, rough, and with a variety of adjunct: cilia, the ring pattern, and so on a variety of scales. These appendage of the shape, size, color and have all kinds of changes. Jungai the edge of the shape is not the same, with young ripe can be completely different shape. After the maturity period can be divided into the general volume, roll back, Shangqiao, such as the extension. There are all-around edge and tidy, while others are not neat or Chengbo Lang-torn. Jungai surface of the cortex. Mycelium in the cortex, with different colors, so Jungai a different color. The following is the cortex bacteria of meat, usually long-filamentous mycelium, and some expansion of the bubble by the cystic component of mycelium. Strain meat color, as well as injured after the color change as a result of the type often vary. General bacteria mostly white meat or white pollution, and some were yellow or red, and so on. Boletus bacteria such as meat and more injured after a blue, black mushrooms thin fold into the red after the first change in black, crimping net fold after injury bacteria become brown, and black wax into a black umbrella after injury. 。

Hymenium body is in the long Jungai have the following part of the hymenium, and some were leafy, Miller called the fold. Some were tube, called the control bacteria. Chengfangshezhuang Junzhe order to connect the central stipe at the top of the outside cover to reach the edge of Miller, hymenium arranged on both sides of the fold in the vaccine, or in the presence of the bacteria around inside the tube.。

座头鲸的英文介绍,急求,谢了

Usually known as the mushroom fungus is in a class, that is, the fruiting bodies of fungi burden. The burden is the fruiting bodies of fungi growing on the ground floor, looks very much like to play in the Village of an umbrella. On the ground floor there is albicans filamentous, spread all over the mycelium, which is the burden of nutrition-related bacteria, that is, non-reproductive organs. To a certain temperature and humidity conditions, to obtain mycelial enough nutrients on the fruit began to take shape. In the early fruiting body as eggs exposed on the ground, rapidly developed into a fruiting body, Jungai, stipe, up bacteria, fungi such as the ring. Mature fruit body shape, size, height, color, texture, and so very different. The large-diameter up to about 40 cm high up to about 50 cm; little less than half centimeters in diameter, 1 cm high, however. It will now be part of the description of the characters are as follows: Jungai fruiting body is the most obvious, like a hat. Wide variety of shapes, there are common bell-shaped, hats shaped, hemispherical, flat-shaped, funnel-shaped, and so on. Jungai color complex, although basically can identify white, yellow, brown, gray, red, green, purple color, and so on, but there are all kinds of deep color, light, light, strong differences are more common Mixed color. Young and old when they cooked the color can be different from the edge of the central government and the color is often the difference. Surface dry, wet, sticky, smooth, rough, and with a variety of adjunct: cilia, the ring pattern, and so on a variety of scales. These appendage of the shape, size, color and have all kinds of changes. Jungai the edge of the shape is not the same, with young ripe can be completely different shape. After the maturity period can be divided into the general volume, roll back, Shangqiao, such as the extension. There are all-around edge and tidy, while others are not neat or Chengbo Lang-torn. Jungai surface of the cortex. Mycelium in the cortex, with different colors, so Jungai a different color. The following is the cortex bacteria of meat, usually long-filamentous mycelium, and some expansion of the bubble by the cystic component of mycelium. Strain meat color, as well as injured after the color change as a result of the type often vary. General bacteria mostly white meat or white pollution, and some were yellow or red, and so on. Boletus bacteria such as meat and more injured after a blue, black mushrooms thin fold into the red after the first change in black, crimping net fold after injury bacteria become brown, and black wax into a black umbrella after injury. 。

Hymenium body is in the long Jungai have the following part of the hymenium, and some were leafy, Miller called the fold. Some were tube, called the control bacteria. Chengfangshezhuang Junzhe order to connect the central stipe at the top of the outside cover to reach the edge of Miller, hymenium arranged on both sides of the fold in the vaccine, or in the presence of the bacteria around inside the tube.。

double是什么意思

Humpback Whale

The Humpback Whale (Megaptera novaeangliae) is a baleen whale. One of the larger rorqual species, adults range in length from 12–16 metres (40–50 ft) and weigh approximately 36,000 kilograms (79,000 lb). The Humpback has a distinctive body shape, with unusually long pectoral fins and a knobbly head. It is an acrobatic animal, often breaching and slapping the water. Males produce a complex whale song, which lasts for 10 to 20 minutes and is repeated for hours at a time. The purpose of the song is not yet clear, although it appears to have a role in mating.。

Found in oceans and seas around the world, Humpback Whales typically migrate up to 25,000 kilometres each year. Humpbacks feed only in summer, in polar waters, and migrate to tropical or sub-tropical waters to breed and give birth in the winter. During the winter, Humpbacks fast and live off their fat reserves. The species' diet consists mostly of krill and small fish. Humpbacks have a diverse repertoire of feeding methods, including the spectacular bubble net fishing technique.。

Like other large whales, the Humpback was and is a target for the whaling industry. Due to over-hunting its population fell by an estimated 90% before a whaling moratorium was introduced in 1966. Stocks of the species have since partially recovered, however entanglement in fishing gear, collisions with ships, and noise pollution also remain concerns. There are at least 70,000 humpback whales worldwide. Once hunted to the brink of extinction, Humpbacks are now sought out by whale-watchers, particularly off parts of Australia and the United States. On November 18, 2007 a Japanese fleet set off for the first time in decades to hunt the humpback in the South Pacific[2].。

Humpback Whales are rorquals (family Balaenopteridae), a family that includes the Blue Whale, the Fin Whale, the Bryde's Whale, the Sei Whale and the Minke Whale. The rorquals are believed to have diverged from the other families of the suborder Mysticeti as long ago as the middle Miocene.[3] However, it is not known when the members of these families diverged from each other.。

Though clearly related to the giant whales of the genus Balaenoptera, the Humpback has been the sole member of its genus since Gray's work in 1846. More recently though, DNA sequencing analysis has indicated both the Humpback and the Gray Whale are close relatives of the Blue Whale, the world's largest animal. If further research confirms these relationships, it will be necessary to reclassify the rorquals.。

The Humpback Whale was first identified as "baleine de la Nouvelle Angleterre" by Mathurin Jacques Brisson in his Regnum Animale of 1756. In 1781, Georg Heinrich Borowski described the species, converting Brisson's name to its Latin equivalent, Balaena novaeangliae. Early in the 19th century Lacépède shifted the Humpback from the Balaenidae family, renaming it Balaenoptera jubartes. In 1846, John Edward Gray created the genus Megaptera, classifying the Humpback as Megaptera longpinna, but in 1932, Remington Kellogg reverted the species names to use Borowski's novaeangliae.[4] The common name is derived from their humping motion while swimming. The generic name Megaptera from the Greek mega-/μεγα- "giant" and ptera/πτερα "wing",[5] refers to their large front flippers. The specific name means "New Englander" and was probably given by Brisson due the regular sightings of Humpbacks off the coast of New England.[4]。

Humpback Whales can easily be identified by their stocky bodies with obvious humps and black dorsal colouring. The head and lower jaw are covered with knobs called tubercles, which are actually hair follicles and are characteristic of the species. The tail flukes, which are lifted high in the dive sequence, have wavy rear edges.[6]。

The long black and white tail fin, which can be up to a third of body length, and the pectoral fins have unique patterns, which enable individual whales to be recognised.[7][8] Several suggestions have been made to explain the evolution of the Humpback's pectoral fins, which are proportionally the longest fins of any cetacean. The two most enduring hypotheses are the higher maneuverability afforded by long fins, or that the increased surface area is useful for temperature control when migrating between warm and cold climates.。

Humpbacks have 270 to 400 darkly coloured baleen plates on each side of the mouth. Ventral grooves run from the lower jaw to the umbilicus about halfway along the bottom of the whale. These grooves are less numerous (usually 16–20) and consequently more prominent than in other rorquals. The stubby dorsal fin is visible soon after the blow when the whale surfaces, but has disappeared by the time the flukes emerge. Humpbacks have a distinctive 3 m (10 ft) bushy blow.。

Newborn calves are roughly the length of their mother's head. A 50' mother would have a 20' newborn weighing in at 2 tons! They are nursed by their mothers for approximately six months, then are sustained through a mixture of nursing and independent feeding for possibly six months more. Some calves have been observed alone after arrival in Alaskan waters. Females reach sexual maturity at the age of five with full adult size being achieved a little later. According to new research, males reach sexual maturity at approximately 7 years of age. Fully grown the males average 15–16 m (49–52 ft), the females being slightly larger at 16–17 m (52–56 ft), with a weight of 40,000 kg (or 44 tons); the largest recorded specimen was 19 m (62 ft) long and had pectoral fins measuring 6 m (20 ft) each.[9] The largest Humpback on record, according to whaling records, was killed in the Caribbean. She was 88 feet long, weighing nearly 90 tons!。

Females have a hemispherical lobe about 15 centimetres (6 in) in diameter in their genital region. This allows males and females to be distinguished if the underside of the whale can be seen, even though the male's penis usually remains unseen in the genital slit. Male whales have distinctive scars on heads and bodies, some resulting from battles over females.。

Females typically breed every two or three years. The gestation period is 11.5 months, yet some individuals can breed in two consecutive years. Humpback Whales were thought to live 50 - 60 years, but new studies using the changes in amino acids behind eye lenses proved another baleen whale, the Bowhead, to be 211 years old. This was an animal taken by the Inuit off Alaska. More studies on ages are currently being done.。

The varying patterns on the Humpback's tail flukes are sufficient to identify an individual. Unique visual identification is not possible in most cetacean species (exceptions include Orcas and Right Whales), so the Humpback has become one of the most-studied species. A study using data from 1973 to 1998 on whales in the North Atlantic gave researchers detailed information on gestation times, growth rates, and calving periods, as well as allowing more accurate population predictions by simulating the mark-release-recapture technique. A photographic catalogue of all known whales in the North Atlantic was developed over this period and is currently maintained by Wheelock College.[10] Similar photographic identification projects have subsequently begun in the North Pacific by SPLASH (Structure of Populations, Levels of Abundance and Status of Humpbacks), and around the world.。

Social structure and courtship：

Humpbacks frequently breach, throwing two thirds or more of their body out of the water and splashing down on their back.。

Humpbacks frequently breach, throwing two thirds or more of their body out of the water and splashing down on their back.。

The Humpback social structure is loose-knit. Usually, individuals live alone or in small transient groups that assemble and break up over the course of a few hours. Groups may stay together a little longer in summer in order to forage and feed cooperatively. Longer-term relationships between pairs or small groups, lasting months or even years, have been observed, but are rare. Recent studies extrapolate feeding bonds observed with many females in Alaskan waters over the last 10 years. It is possible some females may have these bonds for a lifetime. More studies need to be done on this. The range of the Humpback overlaps considerably with many other whale and dolphin species — whilst it may be seen near other species (for instance, the Minke Whale), it rarely interacts socially with them. Humpback calves have been observed in Hawaiian waters playing with bottlenose dolphin calves.。

Courtship rituals take place during the winter months, when the whales migrate towards the equator from their summer feeding grounds closer to the poles. Competition for a mate is usually fierce, and female whales as well as mother-calf dyads are frequently trailed by unrelated male whales dubbed escorts by researcher Louis Herman. Groups of two to twenty males typically gather around a single female and exhibit a variety of behaviours in order to establish dominance in what is known as a competitive pod. The displays may last several hours, the group size may ebb and flow as unsuccessful males retreat and others arrive to try their luck. Techniques used include breaching, spy-hopping, lob-tailing, tail-slapping, flipper-slapping, charging and parrying. "Super pods" have been observed numbering more than 40 males, all vying for the same female. (M. Ferrari et. al)。

Whale song is assumed to have an important role in mate selection; however, scientists remain unsure whether the song is used between males in order to establish identity and dominance, between a male and a female as a mating call, or a mixture of the two. All these vocal and physical techniques have also been observed while not in the presence of potential mates. This indicates that they are probably important as a more general communication tool. Recent studies showed singing males attract other males. Scientists are extrapolating possibilities the singing may be a way to keep the migrating populations connected. (Ferrari, Nicklin, Darling, et. al.) Studies on this are ongoing.。

Feeding：

A group of 15 whales bubble net fishing near Juneau, Alaska。

A group of 15 whales bubble net fishing near Juneau, Alaska。

The species feeds only in summer and lives off fat reserves during winter. Humpback Whales will only feed rarely and opportunistically while in their wintering waters. It is an energetic feeder, taking krill and small schooling fish, such as herring (Clupea harengus), salmon, capelin (Mallotus villosus) and sand lance (Ammodytes americanus) as well as Mackerel (Scomber scombrus), pollock (Pollachius virens) and haddock (Melanogrammus aeglefinus) in the North Atlantic.[11][12][13] Krill and Copepods have been recorded from Australian and Antarctic waters.[14] It hunts fish by direct attack or by stunning them by hitting the water with its flippers or flukes.。

A pair of Humpback Whales feeding by lunging.。

A pair of Humpback Whales feeding by lunging.。

The Humpback has the most diverse repertoire of feeding methods of all baleen whales.[15] Its most inventive technique is known as bubble net fishing: a group of whales blows bubbles while swimming in circles to create a ring of bubbles. The ring encircles the fish, which are confined in an ever-tighter area as the whales swim in a smaller and smaller circles. The whales then suddenly swim upwards through the bubble net, mouths agape, swallowing thousands of fish in one gulp. This technique can involve a ring of bubbles up to 30 m (100 ft) in diameter and the cooperation of a dozen animals. Some of the whales take the task of blowing the bubbles through their blowholes, some dive deeper to drive fish towards the surface, and others herd fish into the net by vocalizing. It is one of the more spectacular acts of collaboration among marine mammals.[16]。

Humpback Whales are preyed upon by Orcas. The result of these attacks is generally nothing more serious than some scarring of the skin, but it is likely that young calves are sometimes killed.[17]。

Song：

Both male and female Humpback Whales can produce sounds, however only the males produce the long, loud, complex "songs" for which the species is famous. Each song consists of several sounds in a low register that vary in amplitude and frequency, and typically lasts from 10 to 20 minutes.[18] Songs may be repeated continuously for several hours; Humpback Whales have been observed to sing continuously for more than 24 hours at a time. As cetaceans have no vocal cords, whales generate their song by forcing air through their massive nasal cavities.。

Whales within an area sing the same song, for example all of the Humpback Whales of the North Atlantic sing the same song, and those of the North Pacific sing a different song. Each population's song changes slowly over a period of years —never returning to the same sequence of notes.[18]。

Scientists are still unsure of the purpose of whale song. Only male Humpbacks sing, so it was initially assumed that the purpose of the songs was to attract females. However, many of the whales observed to approach singing whales have been other males, with the meeting resulting in a conflict. Thus, one interpretation is that the whale songs serve as a threat to other males.[19] Some scientists have hypothesized that the song may serve an echolocative function.[20] During the feeding season, Humpback Whales make altogether different vocalizations, which they use to herd fish into their bubble nets.[21]。

Population and distribution：

The Humpback whale is found in all the major oceans, in a wide band running from the Antarctic ice edge to 65° N latitude, though is not found in the eastern Mediterranean, the Baltic Sea or the Arctic Ocean. There are at least over 70,000 humpback whales worldwide, with 10,000-25,000 in the North Pacific, nearly 12,000 in the North Atlantic, and over 50,000 in the Southern Hemisphere, down from a pre-whaling population of 125,000[citation needed].。

The Humpback is a migratory species, spending its summers in cooler, high-latitude waters, but mating and calving in tropical and sub-tropical waters.[18] An exception to this rule is a population in the Arabian Sea, which remains in these tropical waters year-round.[18] Annual migrations of up to 25,000 kilometres (16,000 statute miles) are typical, making it one of the farthest-travelling of any mammalian species.。

A 2007 study identified seven individual whales wintering off the Pacific coast of Costa Rica as those which had made a trip from the Antarctic of around 8,300 km. Identified by their unique tail patterns, these animals have made the longest documented migration by a mammal.[22]。

In Australia, two main migratory populations have been identified, off the west and east coast respectively. These two populations are distinct with only a few females in each generation crossing between the two groups.[23]。

Whaling：

One of the first attempts to hunt the humpback whale was made by John Smith in 1614 off the coast of Maine. Opportunistic killing of the species is likely to have occurred long before, and it continued with increasing pace in the following centuries. By the 18th century, the commercial value of Humpback Whales had been recognized[citation needed], and they became a common target for whalers for many years.。

By the 19th century, many nations (and the United States in particular), were hunting the animal heavily in the Atlantic Ocean — and to a lesser extent in the Indian and Pacific Oceans. However, it was the introduction of the explosive harpoon in the late 19th century that allowed whalers to accelerate their take. This, coupled with the opening-up of the Antarctic seas in 1904, led to a sharp decline in all whale populations.。

It is estimated that during the 20th century at least 200,000 Humpbacks were taken, reducing the global population by over 90%, with the population in the North Atlantic estimated to have dropped to as low as 700 individuals.[24] To prevent species extinction, a general moratorium on the hunting of Humpbacks was introduced in 1966 and is still in force today. In his book Humpback Whales (1996), Phil Clapham, a scientist at the Smithsonian Institute, said "This wanton destruction of some of the earth's most magnificent creatures [is] one of the greatest of our many environmental crimes."。

By the time the International Whaling Commission (IWC) members agreed on a moratorium on Humpback hunting in 1966, the whales were so scarce that commercial hunting was no longer worthwhile. At this time, 250,000 were recorded killed. However, the true toll is likely to be significantly higher. It is now known that the Soviet Union was deliberately under-recording its kills; the total Soviet Humpback kill was reported at 2,820 whereas the true number is now believed to be over 48,000.[25]。

As of 2004, hunting of Humpback Whales is restricted to a few animals each year off the Caribbean island Bequia in the nation of St. Vincent and the Grenadines.[15] The take is not believed to threaten the local population.。

Conservation:

Internationally this species is considered vulnerable. Most monitored stocks of Humpback Whales have rebounded well since the end of the commercial whaling era,[1] such as the North Atlantic where stocks are now believed to be approaching pre-hunting levels.[29] However, the species is considered endangered in some countries where local populations have recovered slowly, including the United States.[30]。

Today, individuals are vulnerable to collisions with ships, entanglement in fishing gear, and noise pollution.[1] Like other cetaceans, Humpbacks are sensitive to noise and can even be injured by it. In the 19th century, two Humpback Whales were found dead near sites of repeated oceanic sub-bottom blasting, with traumatic injuries and fractures in the ears.[31]。

The ingestion of saxitoxin, a PSP (paralytic shellfish poison) from contaminated mackerel has been implicated in Humpback Whale deaths.[32]。

Some countries are creating action plans to protect the Humpback; for example, in the United Kingdom, the Humpback Whale has been designated as a priority species under the national Biodiversity Action Plan, generating a set of actions to conserve the species. The sanctuary provided by National Parks such as Glacier Bay National Park and Preserve and Cape Hatteras National Seashore, among others, have also become a major factor in sustaining the populations of the species in those areas.[33]。

Although much was known about the Humpback Whale due to information obtained through whaling, the migratory patterns and social interactions of the species were not well known until two separate studies by R. Chittleborough and W. H. Dawbin in the 1960s.[34] Roger Payne and Scott McVay made further studies of the species in 1971.[35] Their analysis of whale song led to worldwide media interest in the species, and left an impression in the public mind that whales were a highly intelligent cetacean species, a contributing factor to the anti-whaling stance of many countries.。

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double意思为一对，一双；双重地；酷似的人；把...对折；变成两倍；增加一倍。

double可作形容词、副词、动词用。

double（双精度浮点型）是计算机使用的一种资料型别。

比起单精度浮点数(float)，double(双精度浮点数)使用64位（8字节）来储存一个浮点数。它可以表示十进制的15或16位有效数字，负值取值范围为-1.7976E+308到-4.94065645841246544E-324，正值取值范围为4.94065645841246544E-324到1.797693E+308一站式出国留学攻略 http://www.offercoming.com。

原文地址：http://www.qianchusai.com/hemispherical-30.html