eye |
truck |
top 10 words in brain distribution (in article): water light form time animal type surface produce cause region |
top 10 words in brain distribution (in article): body time steel type term allow produce common modern refer |
top 10 words in brain distribution (not in article): ice rock drink lamp river flow sea soil state occur |
top 10 words in brain distribution (not in article): church bishop cell form iron blade head century pope roman |
times more probable under eye 30 20 10 6 4 2.5 1.25 1 1.25 2.5 4 6 10 20 30 times more probable under truck (words not in the model) | |
Eyes'" are organs that detect light, and send signals along the optic nerve to the visual and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system. Image-resolving eyes are present in cnidaria, mollusks, chordates, annelids and arthropods. The simplest "eyes", in even unicellular organisms, do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms. From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment. Overview. Complex eyes can distinguish shapes and colors. The visual fields of many organisms, especially predators, involve large areas of binocular vision to improve depth perception; in other organisms, eyes are located so as to maximise the field of view, such as in rabbits and horses. The first proto-eyes evolved among animals 540 million years ago, about the time of the so-called Cambrian explosion. The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in 6 of the thirty-something main phyla. In most vertebrates and some mollusks, the eye works by allowing light to enter it and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for color) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals for vision. The visual signals are then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and often an iris; the relaxing or tightening of the muscles around the iris change the size of the pupil, thereby regulating the amount of light that enters the eye, and reducing aberrations when there is enough light. The eyes of cephalopods, fish, amphibians and snakes usually have fixed lens shapes, and focusing vision is achieved by telescoping the lens — similar to how a camera focuses. Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the details of anatomy, may give either a single pixelated image or multiple images, per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors, which are arranged hexagonally, and which can give a full 360-degree field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an image, creating vision. With each eye viewing a different thing, a fused image from all the eyes is produced in the brain, providing very different, high-resolution images. Possessing detailed hyperspectral color vision, the Mantis shrimp has been reported to have the world's most complex color vision system. Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods, which have soft eyes. The number of lenses in such an eye varied, however: some trilobites had only one, and some had thousands of lenses in one eye. In contrast to compound eyes, simple eyes are those that have a single lens. For example, jumping spiders have a large pair of simple eyes with a narrow field of view, supported by an array of other, smaller eyes for peripheral vision. Some insect larvae, like caterpillars, have a different type of simple eye (stemmata) which gives a rough image. Some of the simplest eyes, called ocelli, can be found in animals like some of the snails, which cannot actually "see" in the normal sense. They do have photosensitive cells, but no lens and no other means of projecting an image onto these cells. They can distinguish between light and dark, but no more. This enables snails to keep out of direct sunlight. In organisms dwelling near deep-sea vents, compound eyes have been secondarily simplified and adapted to spot the infra-red light produced by the hot vents in this way the bearers can spot hot springs and avoid being boiled alive. Evolution. Visual pigments appear to have a common ancestor and were probably involved in circadian rhythms or reproductive timing in simple organisms. Complex vision, associated with dedicated visual organs, or eyes, evolved many times in different lineages. Types of eye. Nature has produced ten different eye layouts — indeed every way of capturing an image has evolved at least once in nature, with the exception of zoom and Fresnel lenses. Eye types can be categorized into "simple eyes", with one concave chamber, and "compound eyes", which comprise a number of individual lenses laid out on a convex surface. Note that "simple" does not imply a reduced level of complexity or acuity. Indeed, any eye type can be adapted for almost any behaviour or environment. The only limitations specific to eye types are that of resolution — the physics of compound eyes prevents them from achieving a resolution better than 1°. Also, superposition eyes can achieve greater sensitivity than apposition eyes, so are better suited to dark-dwelling creatures. Eyes also fall into two groups on the basis of their photoreceptor's cellular construction, with the photoreceptor cells either being cilliated (as in the vertebrates) or rhabdomic. These two groups are not monophyletic; the cnidaira also possess cilliated cells, Pit eyes. Pit eyes, also known as stemma, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eyespot, to allow the organism to deduce the angle of incoming light. Found in about 85% of phyla, these basic forms were probably the precursors to more advanced types of "simple eye". They are small, comprising up to about 100 cells covering about 100 µm. The directionality can be improved by reducing the size of the aperture, by incorporating a reflective layer behind the receptor cells, or by filling the pit with a refractile material. Pinhole eye. The pinhole eye is an "advanced" form of pit eye incorporating these improvements, most notably a small aperture (which may be adjustable) and deep pit. It is only found in the nautiloids. Without a lens to focus the image, it produces a blurry image, and will blur out a point to the size of the aperture. Consequently, nautiloids can't discriminate between objects with an angular separation of less than 11°. Shrinking the aperture would produce a sharper image, but let in less light. Spherical lensed eye. The resolution of pit eyes can be greatly improved by incorporating a material with a higher refractive index to form a lens, which may greatly reduce the blur radius encountered — hence increasing the resolution obtainable. The most basic form, still seen in some gastropods and annelids, consists of a lens of one refractive index. A far sharper image can be obtained using materials with a high refractive index, decreasing to the edges — this decreases the focal length and thus allows a sharp image to form on the retina. This also allows a larger aperture for a given sharpness of image, allowing more light to enter the lens; and a flatter lens, reducing spherical aberration. Such an inhomogeneous lens is necessary in order for the focal length to drop from about 4 times the lens radius, to 2.5 radii. Heterogeneous eyes have evolved at least eight times — four or more times in gastropods, once in the copepods, once in the annelids and once in the cephalopods. No aquatic organisms possess homogeneous lenses; presumably the evolutionary pressure for a heterogeneous lens is great enough for this stage to be quickly "outgrown". This eye creates an image that is sharp enough that motion of the eye can cause significant blurring. To minimize the effect of eye motion while the animal moves, most such eyes have stabilizing eye muscles. The ocelli of insects bear a simple lens, but their focal point always lies behind the retina; consequently they can never form a sharp image. This capitulates the function of the eye. Ocelli (pit-type eyes of arthropods) blur the image across the whole retina, and are consequently excellent at responding to rapid changes in light intensity across the whole visual field — this fast response is further accelerated by the large nerve bundles which rush the information to the brain. Focussing the image would also cause the sun's image to be focussed on a few receptors, with the possibility of damage under the intense light; shielding the receptors would block out some light and thus reduce their sensitivity. This fast response has led to suggestions that the ocelli of insects are used mainly in flight, because they can be used to detect sudden changes in which way is up (because light, especially UV light which is absorbed by vegetation, usually comes from above). Weaknesses. One weakness of this eye construction is that chromatic aberration is still quite high — although for organisms without color vision, this is a very minor concern. A weakness of the vertebrate eye is the blind spot which results from a gap in the retina where the optic nerve exits at the back of the eye; the cephalopod eye has no blind spot as the retina is in the opposite orientation. Multiple lenses. Some marine organisms bear more than one lens; for instance the copeopod "Pontella" has three. The outer has a parabolic surface, countering the effects of spherical aberration while allowing a sharp image to be formed. "Copilla'"s eyes have two lenses, which move in and out like a telescope. Such arrangements are rare and poorly understood, but represent an interesting alternative construction. An interesting use of multiple lenses is seen in some hunters such as eagles and jumping spiders, which have a refractive cornea (discussed next): these have a negative lens, enlarging the observed image by up to 50% over the receptor cells, thus increasing their optical resolution. Refractive cornea. In the eyes of most terrestrial vertebrates (along with spiders and some insect larvae) the vitreous fluid has a higher refractive index than the air, relieving the lens of the function of reducing the focal length. This has freed it up for fine adjustments of focus, allowing a very high resolution to be obtained. As with spherical lenses, the problem of spherical aberration caused by the lens can be countered either by using an inhomogeneous lens material, or by flattening the lens. Flattening the lens has a disadvantage: the quality of vision is diminished away from the main line of focus, meaning that animals requiring all-round vision are detrimented. Such animals often display an inhomogeneous lens instead. As mentioned above, a refractive cornea is only useful out of water; in water, there is no difference in refractive index between the vitreous fluid and the surrounding water. Hence creatures which have returned to the water — penguins and seals, for example — lose their refractive cornea and return to lens-based vision. An alternative solution, borne by some divers, is to have a very strong cornea. Reflector eyes. An alternative to a lens is to line the inside of the eye with mirrors", and reflect the image to focus at a central point. The nature of these eyes means that if one were to peer into the pupil of an eye, one would see the same image that the organism would see, reflected back out. Many small organisms such as rotifers, copeopods and platyhelminths use such organs, but these are too small to produce usable images. Some larger organisms, such as scallops, also use reflector eyes. The scallop "Pecten" has up to 100 millimeter-scale reflector eyes fringing the edge of its shell. It detects moving objects as they pass successive lenses. Compound eyes. A compound eye may consist of thousands of individual photoreception units. The image perceived is a combination of inputs from the numerous ommatidia (individual "eye units"), which are located on a convex surface, thus pointing in slightly different directions. Compared with simple eyes, compound eyes possess a very large view angle, and can detect fast movement and, in some cases, the polarization of light. Because the individual lenses are so small, the effects of diffraction impose a limit on the possible resolution that can be obtained. This can only be countered by increasing lens size and number — to see with a resolution comparable to our simple eyes, humans would require compound eyes which would each reach the size of their head. Compound | A truck'" is a type of motor vehicle commonly used for carrying goods and materials. Some light trucks are relatively small, similar in size to a passenger automobile. Commercial transportation or fire trucks can be quite large and can also serve as a platform for specialized equipment. Etymology. The word "truck" possibly derives from the Greek "trochos" (τροχός =wheel). In North America, certain kinds of big wheels were called "trucks". When the gasoline-engine driven trucks came into fashion, these were called "motor trucks." International variance. In the United States and Canada "truck" is usually reserved for commercial vehicles larger than normal cars, and for pickups and other vehicles having an open load bed. In the United Kingdom and the Republic of Ireland, "lorry" is used as well as "truck", but only used for the medium and heavy types (see below); "i.e." a van, a pickup or an off-road four-wheel drive vehicle such as a Jeep would never be regarded as a lorry in these countries, unlike in the United States (it should be noted, however, that the term lorry is not used in the United States). The same applies to the initials "HGV" (for Heavy Goods Vehicle) which is basically synonymous with "lorry". The word "truck" is also accepted in these countries, and can apply to large vans as well as to lorries ("i.e." its scope is slightly wider). In the UK vernacular, "wagon" is still commonly used to describe various larger vehicles. Though the US term station wagon is occasionally used in the UK, it can cause confusion (despite retaining the US definition), so the societal term estate car remains widely popular. "Lorry" is also used in Hong Kong. In South Africa, the word "kombi" is used, based on its Afrikaans equivalent. The word "lorry" is also used in Cambodia, although here it can refer to a train. In Australia and New Zealand, a pickup truck (a relatively small, usually car- or van-derived vehicle, with an open back body) is called a ute'" (short for "utility") and the word "truck" or "lorry" is reserved for larger vehicles. Other languages have loanwords based on these terms, such as the Malay language and the Spanish language in northern Mexico. A commonly understood term for truck across many European countries is "'camion'". Camion is also used in Quebec to identify trucks in French. Additionally, from the German language the initials "PKW" ("'P'"ersonen"'K'"raft"'W'"agen or passenger carrying vehicle) for a car van or small truck) and "LKW" ("'L'"ast"'K'"raft"'W'"agen or cargo load freight carrying vehicle) for larger trucks are understood. In U.S. English the word "truck" is used in the names of particular types of truck, such as a "fire truck" or "tanker truck". Note that in British English these would be a "fire engine" and "tanker" respectively. Driving. In the United States a commercial driver's license is required to drive any type of vehicle weighing 26,001 lbs (11,800 kg) or more. In the United Kingdom there are complex rules; as an overview, to drive a vehicle weighing more than 7,500 kg for commercial purposes requires a specialist license (the type varies depending on the use of the vehicle and number of seats). For licenses first acquired after 1997, that weight was reduced to 3,500 kg, not including trailers. In the Australia a truck driving license is required for any motor vehicle with a GVM exceeding 4500 kg. The motor vehicles classes are further expanded as "'LR/MR'" (Light Medium rigid up to 8000 kg GVM + trailer to maximum GCM 8000 kg), "'HR'" (Heavy Rigid +trailer up to GCM 9000 kg), "'HC'" (Heavy Combination, a typical prime mover +semi trailer combination) and the "'MC'" (Multi Combination e.g B Doubles Road trains). There is also a heavy vehicle transmission condition for a licence class HR, HC or MC in a vehicle fitted with an automatic or synchromesh transmission, driver’s licence will restrict to vehicles of that class fitted with a synchromesh or automatic transmission. To have the condition removed, a person needs to pass a practical driving test in a vehicle with non synchromesh transmission (constant mesh or crash box). Engine. The oldest truck was built in 1896 by Gottlieb Daimler. Small trucks such as SUVs or pickups, and even light medium-duty trucks in North America and Russia will use gasoline engines. Most heavier trucks use four stroke turbo intercooler diesel engines. Huge off-highway trucks use locomotive-type engines such as a V12 Detroit Diesel two stroke engine. North American manufactured highway trucks almost always use an engine built by a third party, such as CAT, Cummins, or Detroit Diesel. The only exceptions to this are Volvo and its subsidiary Mack Trucks, which are available with their own engines. Freightliner Trucks, Sterling Trucks and Western Star, subsidiaries of Daimler AG, are available with Mercedes-Benz and Detroit Diesel engines. Trucks and buses built by Navistar International usually also contain International engines. The Swedish manufacturer Scania claims they stay away from the U.S. market because of this third party tradition. In the European Union all new truck engines must comply with Euro 5 regulations. Drivetrain. Small trucks use the same type of transmissions as almost all cars, having either an automatic transmission or a manual transmission with synchronisers. Bigger trucks often use manual transmissions without synchronisers, saving bulk and weight, although synchromesh transmissions are used in larger trucks as well. Transmissions without synchronizers, known as "crash boxes", require double-clutching for each shift, (which can lead to repetitive motion injuries), or a technique known colloquially as "floating," a method of changing gears which doesn't use the clutch, except for starts and stops, due to the physical effort of double clutching, especially with non power assisted clutches, faster shifts, and less clutch wear. Double-clutching allows the driver to control the engine and transmission revolutions to synchronize, so that a smooth shift can be made, "e.g.," when upshifting, the accelerator pedal is released and the clutch pedal is depressed while the gear lever is moved into neutral, the clutch pedal is then released and quickly pushed down again while the gear lever is moved to the next highest gear. Finally, the clutch pedal is released and the accelerator pedal pushed down to obtain required engine speed. Although this is a relatively fast movement, perhaps a second or so while transmission is in neutral, it allows the engine speed to drop and synchronize engine and transmission revolutions relative to the road speed. Downshifting is performed in a similar fashion, except the engine speed is now required to increase (while transmission is in neutral) just the right amount in order to achieve the synchronization for a smooth, non-collision gear change. "Skip changing" is also widely used; in principle operation is the same as double-clutching, but it requires neutral be held slightly longer than a single gear change. Common North American setups include 9, 10, 13, 15, and 18 speeds. Automatic and semi-automatic transmissions for heavy trucks are becoming more and more common, due to advances both in transmission and engine power. In Europe 8, 10, 12 and 16 gears are common on larger trucks with manual transmission, while automatic or semiautomatic transmissions would have anything from 5 to 12 gears. Almost all heavy truck transmissions are of the "range and split" (double H shift pattern) type, where range change and so-called half gears or splits are air operated and always preselected before the main gear selection. More new trucks in Europe are being sold with automatic or semi-automatic transmissions. This may be due the fuel consumption can be lowered and truck durability improved. The primary reason perhaps is the fact that such transmissions give a driver more time to concentrate on the road and traffic conditions. Frame. A truck frame consists of two parallel boxed (tubular) or C-shaped rails, or beams, held together by crossmembers. These frames are referred to as ladder frames due to their resemblance to a ladder if tipped on end. The rails consist of a tall vertical section (two if boxed) and two shorter horizontal flanges. The height of the vertical section provides opposition to vertical flex when weight is applied to the top of the frame (beam resistance). Though typically flat the whole length on heavy duty trucks, the rails may sometimes be tapered or arched for clearance around the engine or over the axles. The holes in rails are used either for mounting vehicle components and running wires and hoses, or measuring and adjusting the orientation of the rails at the factory or repair shop. Though they may be welded, crossmembers are most often attached to frame rails by bolts or rivets. Crossmembers may be boxed or stamped into a c-shape, but are most commonly boxed on modern vehicles, particularly heavy trucks. The frame is almost always made of steel, but can be made (whole or in part) of aluminum for a lighter weight. A tow bar may be found attached at one or both ends, but heavy trucks almost always make use of a fifth wheel hitch. Environmental effects. Trucks contribute to air, noise, and water pollution similarly to automobiles. Trucks may emit lower air pollution emissions than cars per pound of vehicle mass, although the absolute level per vehicle mile traveled is higher and diesel particulate matter is especially problematic for health. With respect to noise pollution trucks emit considerably higher sound levels at all speeds compared to typical car; this contrast is particularly strong with heavy-duty trucks. There are several aspects of truck operations that contribute to the overall sound that is emitted. Continuous sounds are those from tires rolling on the roadway and the constant hum of their diesel engines at highway speeds. Less frequent noises, but perhaps more noticeable, are things like the repeated sharp whine of a turbocharger on acceleration or the abrupt blare of an exhaust brake when traversing a downgrade. There has been noise regulation put in place to help control where and when the use of engine braking is allowed. Concerns have been raised about the effect of trucking on the environment, particularly as part of the debate on global warming. In the period from 1990 to 2003, carbon dioxide emissions from transportation sources increased by 20%, despite improvements in vehicle fuel efficiency. In 2005, transportation accounted for 27% of U.S. greenhouse gas emission, increasing faster than any other sector. Between 1985 and 2004, in the U.S., energy consumption in freight transportation grew nearly 53%, while the number of ton-miles carried increased only 43%. "Modal shifts account for a nearly a 23% increase in energy consumption over this period. Much of this shift is due to a greater fraction of freight ton-miles being carried via truck and air, as compared to water, rail, and pipelines." According to a 1995 U.S. Government estimate, the energy cost of carrying a ton of freight a distance of one kilometer averages 337 kJ for water, 221 kJ for rail, 2 000 kJ for trucks and nearly 13 000 kJ for air transport. Many environmental organizations favor laws and incentives to encourage the switch from road to rail, especially in Europe. The European Parliament is moving to ensure that charges on heavy-goods vehicles should be based in part on the air and noise pollution they produce and the congestion they cause, according to legislation approved by the Transport Committee The Eurovignette scheme has been proposed whereby new charges would be potentially levied against things such as noise and air pollution and also weight related damages from the lorries themselves Commercial insurance. Primary Liability Insurance coverage protects the truck from damage or injuries to other people as a result of a truck accident. This truck insurance coverage is mandated by U.S. state and federal agencies and proof of coverage is required to be sent to them. Insurance coverage limits range from $35,000 to $1,000,000. Pricing is dependent on region, driving records, and history of the trucking operation. Motor Truck Cargo insurance protects the transporter for his responsibility in the event of damaged or lost freight. The policy is purchased with a maximum load limit per vehicle. Cargo insurance coverage limits can range from $10,000 to $100,000 or more. Pricing for this insurance is mainly dependent on the type of cargo being hauled. Truck shows. In the UK, three truck shows are popular -Shropshire Truck Show in Oswestry Showground during May, The UK Truck Show held in June at Santa Pod Raceway and FIA European Drag Racing Championships from the home of European Drag-Racing. The UK Truck Show features drag-racing with 6-ton trucks from the British Truck Racing Association, plus other diesel-powered entertainment. Truck Shows provide operators with an opportunity to win awards for their trucks. |