Paralysis is the complete loss of muscle function for one or more muscle groups. Major causes are stroke, trauma, poliomyelitis, amyotrophic lateral sclerosis (ALS), botulism, spina bifida, multiple sclerosis, and Guillain-Barré syndrome. Paralysis is most often caused by damage to the nervous system or brain, especially the spinal cord. Paralysis often includes loss of feeling in the affected area.

Paralysis may be localized, or generalized, or it may follow a certain pattern. For example, localized paralysis occurs in Bell’s palsy where one side of the face may be paralysed due to inflammation of the facial nerve on that side. Patients with stroke may be weak throughout their body (global paralysis) or have hemiplegia (weakness on one side of the body) or other patterns of paralysis depending on the area of damage in the brain. Other patterns of paralysis arise due to different lesions and their sequelae. For example, lower spinal cord damage from a severe back injury may result in paraplegia, while an injury higher up on the spinal cord, such as a neck injury, can cause quadriplegia.

Most paralyses caused by nervous system damage are constant in nature; however, there are forms of periodic paralysis, including sleep paralysis, which are caused by other factors.

Poisons that interfere with nerve function, such as curare, can also cause paralysis.

Alternative Fuel

Alternative fuel is any material or substance, other than petroleum (oil), which is consumed to provide energy to power an engine. Some alternative fuels are biodiesel, ethanol, butanol, chemically stored electricity (batteries and fuel cells), hydrogen, methane, natural gas, wood, and vegetable oil. The need for the development of alternative fuel sources has been growing due to concerns about the environment and that the production of oil will no longer supply the demand.

In a battery or fuel cell powered vehicle, the “fuel” is the set of chemicals which is oxidized and reduced to provide the electricity. In some circumstances, however, electricity may be provided directly to a mobile electric engine, such as an electrified trolley or train, or a magnetically levitated train. In such cases, electricity itself may be treated as an alternative “fuel,” since it replaces fuel energy used in transportation.

Black Market

The black market or underground market is the part of economic activity involving illegal dealings, typically the buying and selling of merchandise or services (for example sexual services in many countries) illegally. The goods may be inherently illegal (e.g. weapons or illegal drugs); the merchandise may be stolen; or the merchandise may be otherwise legal goods sold illicitly to avoid tax payments or licensing requirements, such as cigarettes or unregistered firearms. It is so called because “black economy” or “black market” affairs are conducted outside the law, and so are necessarily conducted “in the dark”, out of the sight of the law.

Black markets develop when the state places restrictions on the production or provision of goods and services that come into conflict with market demands. These markets prosper, then, when state restrictions are heavy, such as during a period of prohibition, price controls and/or rationing. However, black markets are normally present in any given economy.

Black Market Price

As a result of an increase in government restrictions, black market prices for the relevant products will rise, as said restrictions represent a decrease in supply and an increase in risk on the part of the suppliers, sellers, and any and all middlemen. According to the theory of supply and demand, a decrease in supply-making the product more scarce-will increase prices, other things being equal. Similarly, increased enforcement of restrictions will increase prices for the same reason.

Goods acquired illegally can take one of two price levels. They may be less expensive than (legal) market prices because the supplier did not incur the normal costs of production or pay the usual taxes. Alternatively, illegally supplied products may be more expensive than normal prices, because the product in question is difficult to acquire or produce and may not be available legally.

In the former case, however, most people are likely to continue to purchase the products in question from legal suppliers, for a number of reasons:

  • The consumer may feel that the black market supplier conducts business immorally (although this criticism can extend to legal suppliers too).
  • The consumer may-justifiably-trust legal suppliers more, as they are both easier to contact in case of faults in the product and easier to hold accountable.
  • In some countries, it is a criminal offense to handle stolen goods, a factor which will discourage buyers.

In the latter case of a black market for goods which are simply unavailable through legal channels, black markets will thrive if consumer demand nonetheless continues. In the case of the legal prohibition of a product viewed by large segments of the society as harmless, such as alcohol under prohibition in the United States, the black market will prosper, and the black marketeers often reinvest profits in a widely diversified array of illegal activity well beyond the original “harmless” item.

Black market prices can be reduced by removing the relevant legal restrictions, thus increasing supply. People who advocate this may believe that governments should recognize fewer crimes in order to focus law enforcement effort on the most treatable dangers to society. However, this can be seen by some people as the equivalent of legalizing crime in order to reduce the number of “official” criminals-in other words, a concession that in their view only makes matters worse. Alternatively, the government could attempt to decrease demand. However, this is economically out of fashion and not as simple a process as decreasing supply.

The Term “Black Market” also applies to illegal monetary exchange outside the authorized institutes – Banks or Legal Exchange Offices.

Examples of Black Markets

The Prohibition period in the early twentieth century in the United States is a classic example of black market activity. Many organized crime groups took advantage of the lucrative opportunities in the resulting black market in banned alcohol production and sales. Since much of the populace did not view drinking alcohol as a particularly harmful activity that ought to be legally banned, illegal speakeasies prospered, and organizations such as the Mafia grew tremendously more powerful through their black market activities distributing alcohol.

Another classic example is Burma under the rule of Ne Win. Under his “Burmese Way to Socialism”, the country became one of the poorest in the world, and only the black market and rampant smuggling supplied the people’s needs.

Nowadays in many countries, it is argued a “war on drugs” has created a similar effect for drugs such as marijuana, heroin and cocaine. Despite ongoing law enforcement efforts to intercept illegal drug supplies, demand remains high, encouraging organized criminal groups to ensure their availability. While law enforcement efforts often capture distributors of illegal drugs, the high demand for such drugs ensures that black market prices will simply rise in response to the decrease in supply-encouraging new distributors to enter the market in a perpetual cycle.

Similarly, since prostitution is illegal in many places and yet market demand for the services of prostitutes remains high, a black market usually develops.

Black markets can also form near when neighboring jurisdictions have substantially different tax rates on similar products. Products that are commonly smuggled to fuel these black markets include alcohol and tobacco.

Black markets flourish in most countries during wartime. The rationing and price controls enforced in many countries during World War II encouraged widespread black market activity. Due to severe shortages of consumer goods, black markets thrived in communist Eastern Europe and the Soviet Union.

Diffuse Axonal Injury

Diffuse axonal injury (DAI) is one of the most common and devastating types of brain injury, occurring in almost half of all cases of severe head trauma. It is a type of diffuse brain injury, meaning that damage occurs over a more widespread area than in focal brain injury. DAI, which refers to extensive lesions in white matter tracts, is one of the major causes of unconsciousness and persistent vegetative state after head trauma.

Though diffuse axonal injury seldom leads to death, the outcome is frequently coma with over 90% of patients with severe DAI never regaining consciousness. Those that do wake up often remain significantly impaired.

Diffuse Axonal Injury Mechanism

Unlike brain trauma that occurs due to direct impact and deformation of the brain, DAI is the result of traumatic shearing forces that occur when the head is rapidly accelerated or decelerated, as may occur in auto accidents, falls, and assaults. It usually results from twisting or rotational forces (angular momentum), rather than forward and back impacts linear momentum. Car accidents are the most frequent causes of DAI, with sports accidents and child abuse also common causes.

The major cause of damage in DAI is the tearing of axons, the neural processes that allow one neuron to communicate with another. Tracts of axons, which appear white due to myelination, are referred to as white matter. Acceleration causes shearing injury, which refers to damage inflicted as tissue slides over other tissue. When the brain is accelerated, parts of differing densities and distances from the axis of rotation slide over one another, stretching axons that traverse junctions between areas of different density, especially gray-white matter junctions. Two thirds of DAI lesions occur in areas where grey and white matter meet.

Diffuse Axonal Injury Characteristics

Patients typically have several focal white matter lesions of variable size (1-15 mm) in a characteristic distribution. Areas most vulnerable to injury are the frontal and temporal lobes. Other common locations for DAI include the white matter in the cerebral cortex, the corpus callosum, the superior cerebral peduncles, basal ganglia, thalamus, and deep hemispheric nuclei. These areas may be more easily damaged because of the difference in density between them and the rest of the brain.

Diffuse Axonal Injury Diagnosis and Treatment

DAI is difficult to detect since it does not show up well on CT scans or with other macroscopic imaging techniques. However, Diffuse Axonal Injury does show up microscopically. Axonal damage in DAI is largely a result of secondary biochemical cascades, and has a delayed onset, so a person with DAI who initially appears well may deteriorate later. Thus injury is frequently more severe than is realized, and medical professionals must suspect DAI in any patients whose CT scans appear normal but who have symptoms like unconsciousness.

MRI is more sensitive and 30% of head injured patients with normal head CT scans have signs of DAI on MRI. But MRI may also miss DAI, because it identifies the injury using signs of edema, which may not be present.

DAI is classified in grades based on severity of the injury. In Grade I, widespread axonal damage is present but no focal abnormalities are seen. In Grade II, damage found in Grade I is present in addition to focal abnormalities, especially in the corpus callosum. Grade III damage encompasses both Grades I and II in addition to rostral brain stem injury and often tears in the tissue.

DAI currently lacks a specific treatment beyond what is done for any type of head injury, including stabilizing the patient and trying to limit increases in intracranial pressure (ICP).

Slip Angle

In car handling, slip angle is the angle between a rolling wheel’s actual direction of travel and the direction towards which it is pointing (i.e., the angle of the vector sum of wheel translational velocity v and sideslip velocity u). This slip angle results in a force perpendicular to the wheel’s direction of travel — the cornering force. This cornering force increases approximately linearly for the first few degrees of slip angle, then increases non-linearly to a maximum before beginning to decrease. This is directly analogous to the Coefficient of lift in Aerodynamics.

A non-zero slip angle arises because of deformation in the tire carcass and tread. As the tire rotates, the friction between the contact patch and the road result in individual tread ‘elements’ (infinitely small sections of tread) remaining stationary with respect to the road. If a side-slip velocity u is introduced, the contact patch will be deformed. As a tread element enters the contact patch the friction between road and tire means that the tread element remains stationary, yet the tire continues to move laterally. This means that the tread element will be ‘deflected’ sideways. In reality it is the tire/wheel that is being deflected away from the stationary tread element, but convention is for the co-ordinate system to be fixed around the wheel mid-plane.

As the tread element moves through the contact patch it will be deflected further from the wheel mid-plane:

Slip Angle

Slip Angle

This deflection gives rise to the slip angle, and to the cornering force.

Because the forces exerted on the wheels by the weight of the vehicle are not distributed equally, the slip angles of each tire will be different. The ratios between the slip angles will determine the vehicle’s behavior in a given turn. If the ratio of front to rear slip angles is greater than 1:1, the vehicle will tend to understeer, while a ratio of less than 1:1 will produce oversteer. Actual instantaneous slip angles depend on many factors, including the condition of the road surface, but a vehicle’s suspension can be designed to promote specific dynamic characteristics. A principal means of adjusting developed slip angles is to alter the relative roll couple (the rate at which weight transfers from the inside to the outside wheel in a turn) front to rear by varying the relative amount of front and rear lateral load transfer. This can be achieved by modifying the height of the roll centers, or by adjusting roll stiffness, either through suspension changes or the addition of an anti-roll bar.

Opposite Lock

Opposite lock is a colloquial term used to mean the deliberate use of oversteer to turn a vehicle rapidly without losing momentum. It is typified by the classic rallying style of rear-wheel drive cars, where a car appears to travel around a tight bend sideways. This technique can also be used for front wheel drive vehicles and is referred to as drifting (not to be confused with the sport) in North America.

The term “opposite lock” refers to the position of the steering wheel during the maneuver, which is turned in the opposite direction to that of the bend.

The technique works best on loose surfaces where the friction between the tires and the road is not too high, but can also be used on asphalt or other surfaces with high friction if the vehicle has enough power to maintain speed. In this case a light tire pressure increase is recommended to avoid problems during or after manoeuvres.

Before entry to the bend, the car is turned towards the bend slightly, but quickly, so as to cause a rotating motion that induces the rear of the car to slide outwards. Power is applied which applies further sideways movement. At the same time, opposite lock steering is applied to keep the car on the desired course. As the car reaches the bend it will have already turned through most of the needed angle, travelling sideways and losing some speed as a result. A smooth application of power at this point will accelerate the car into the bend and then through it, gradually removing the sideways component of travel. Overall, the bend will have been negotiated much faster than driving through it in a normal manner. In skilled hands, the result is a dramatic and fluid motion which looks incredibly natural. When executed poorly, the result is often the complete opposite.

For front-wheel drive vehicles, there is much less natural tendency for the rear wheels to break traction because they are not transmitting power, so often such vehicles are set up with a strong bias to the rear brakes, allowing the driver to control traction using the brake pedal. The brake bias (front/rear) may be continually controllable by the driver using a hand lever. Left-foot braking is the favoured technique for using opposite lock in a front drive vehicle.

A related technique is the handbrake turn, in which the rear wheels are deliberately locked in order to break the friction between the tires and the road, allowing the car to be spun around a very tight bend or junction, etc.

Light Truck

Light truck is a vehicle classification for trucks or truck-based vehicles with a payload capacity of less than 4,000 pounds.

Fuel Efficiency in the United States

The United States government uses light truck as a vehicle class in regulating fuel economy through the Corporate Average Fuel Economy standard. The class includes vans, minivans, sport utility vehicles, and pickup trucks.

Light trucks have lower fuel economy standards than cars under the premise that these vehicles are used for more utilitarian purposes than normal passenger transportation.

Since light trucks sold in the United States are increasingly being used for normal passenger transportation, some have advocated applying higher economy standards to light trucks that are not used for utilitarian purposes. One argument in support of this is that light trucks are sometimes based on automobile chassis. Crossover SUVs are a common example.

Monocoque or Unibody

Monocoque (French for “single shell”) or unibody is a construction technique that uses the external skin of an object to support some or most of the load on the structure. This stands in contrast with using an internal framework (or truss) that is then covered with a non-load-bearing skin. Monocoque construction was first widely used in aircraft, starting in the 1930s, and is the predominant automobile construction technology today.

Monocoque or Unibody Automobile Construction

The first automotive application of the monocoque technique was 1923’s Lancia Lambda. Chrysler and Citroën built the first mass-produced monocoque vehicles, both in 1934, with the innovative Chrysler Airflow and the Traction Avant, respectively. The popular Volkswagen Beetle also used a semi-monocoque body (its frame required the body for support) in 1938.

NSU (NSU Prinz) also built monocoque automobiles.

In the post-war period the technique became more widely used. The Alec Issigonis Morris Minor of 1948 featured a monocoque body. The Ford Consul introduced an evolution called unit body or unibody. In this system, separate body panels are still used but are bolted to a monocoque body-shell. Spot welded unibody construction is now the dominant technique in automobiles, though some vehicles (particularly trucks) still use the older body-on-frame technique.

Some American automobiles, such as the 1967 Chevrolet Camaro, used a compromise design with a partial monocoque combined with a subframe carrying the front end and powertrain. The intention was to provide some of the rigidity and strength of a unibody while easing manufacture, although the results were mixed, in large part because the powertrain subframe contained the greatest single portion of the vehicle’s overall mass, and thus movement of the subframe relative to the rest of the body could cause distortion and vibration. Subframes or partial subframes are still sometimes employed in otherwise monocoque construction, typically as a way of isolating the vibration and noise of powertrain or suspension components from the rest of the vehicle.

In automobiles, it is common to see true monocoque frames, where the structural members around the window and door frames are built by folding the skin material several times. In these situations the main concerns are spreading the load evenly, having no holes for corrosion to start, and reducing the overall workload. Compared to older techniques, in which a body is bolted to a frame, monocoque cars are less expensive and stronger.

Monocoque design is so sophisticated that windshield and rear window glass now often make an important contribution to the designed structural strength of automobiles.


Traction refers to the friction between a drive member and the surface it moves upon, where the friction is used to provide motion.

For the purposes of driving a wheeled vehicle, high friction is generally desired, as it provides a more positive connection between the driving and driven members. In contrast, motion in a geared mechanism is provided by interference, and friction is usually detrimental because the gear mechanism has intrinsic sliding, and sliding under friction causes heating losses.

Traction between two surfaces usually depends on several factors including:

  • Material properties of each surface
  • Macroscopic and microscopic shape or “roughness”
  • Force of contact
  • Area of contact
  • Contaminants at the material boundary including lubricants and adhesives

Corporate Average Fuel Economy (CAFE)

The Corporate Average Fuel Economy (CAFE) regulations in the United States, first enacted by Congress in 1975, exist to regulate and improve the average fuel economy of cars and light trucks (trucks, vans and sport utility vehicles) sold in the U.S. in the wake of the 1973 Arab Oil Embargo. It is the sales-weighted average fuel economy, expressed in miles per gallon (mpg), of a manufacturer’s fleet of passenger cars or light trucks with a gross vehicle weight rating (GVWR) of 8,500 pounds (3,856 kg) or less, manufactured for sale in the United States, for any given model year. The National Highway Traffic Safety Administration (NHTSA) and Environmental Protection Agency (EPA) regulate CAFE standards.

If the average fuel economy of a manufacturer’s annual car or truck production falls below the defined standard, the manufacturer must pay a penalty, currently $5.50 per 0.1 mpg under the standard, multiplied by the manufacturer’s total production for the U.S. domestic market.

CAFE – Calculation

For the purposes of CAFE, a manufacturer’s car output is divided into a domestic fleet (vehicles with more than 75% U.S., Canadian or (after the passage of NAFTA) Mexican content) and a foreign fleet (everything else). Each of these fleets must separately meet the requirements. This requirement was designed to benefit the American automobile industry, but it is regarded as having little effect and the possibility of removing the two fleet rule is being considered. The two fleet rule for light trucks was removed in 1996.

Alternative fuel vehicles are treated as if they are substantially more fuel efficient, as an incentive to develop alternative fuel vehicles.

Manufacturers are also allowed to earn CAFE “credits” in any year they exceed CAFE requirements, which they may use to offset deficiencies in other years. CAFE credits can be applied to the three years previous or three years subsequent to the year in which they are earned. The reason for this requirement is so that manufacturers are not penalized for occasionally (due to market conditions, for example) failing the targets, but only for persistent failure to meet them.

CAFE – Current Standards

Cars and light trucks are considered separately for CAFE and are held to different standards. As of early 2004, the average for cars must exceed 27.5 mpg and the light truck average must exceed 20.3 mpg. Trucks under 8500 lb must average 22.5 mpg in 2008, 23.1 mpg in 2009, and 23.5 mpg in 2010. After this, new rules set varying targets based on truck size and class.

Overall fuel economy for cars and light trucks in the U.S. market reached its highest level in 1987, when manufacturers managed 22.1 mpg (10.6 L/100 km). The average in 2004 was 20.8 mpg. In that time, vehicles increased in size from an average of 3,220 pounds to 4,066 lb (1,461 kg to 1,844 kg).

A number of manufacturers choose to pay CAFE penalties rather than attempt to comply with the regulations. As of model year 2002, BMW, DaimlerChrysler (import fleet only), Fiat, Lotus and Porsche failed the automobile CAFE requirement, while BMW and Volkswagen failed to meet the light truck requirement.

CAFE – Future Rules and Standards

The CAFE rules for trucks were officially amended at the end of March, 2006. These changes would segment truck fleets by vehicle size and class as of 2011. All SUVs and passenger vans would now have to comply with CAFE standards regardless of size, but some large pickup trucks and cargo vans would remain exempt.

The fuel economy for a vehicle will be dictated by its “footprint” – the product of its wheelbase and track. Some critics point out that this may have the unintended consequence of pushing manufacturers to make ever-larger vehicles to avoid strict economy standards.

CAFE – Criticism

The CAFE standards have come under attack by think tanks such as the Heritage Foundation and the Competitive Enterprise Institute, primarily on the basis that the cheapest way for automotive manufacturers to increase mileage is to reduce vehicle weight, which makes vehicles inherently less safe in accidents (this point is disputed however). Both groups note almost an exact correlation between increased CAFE standards and increased highway deaths (although correlation does not prove causation).