Cobalt

Cobalt is a chemical element with symbol Co and atomic number 27. Like nickel, cobalt in the Earth's crust is found only in chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.

Cobalt-based blue pigments (cobalt blue) have been used since ancient times for jewelry and paints, and to impart a distinctive blue tint to glass, but the color was later thought by alchemists to be due to the known metal bismuth. Miners had long used the name kobold ore (German for goblin ore) for some of the blue-pigment producing minerals; they were so named because they were poor in known metals, and gave poisonous arsenic-containing fumes upon smelting. In 1735, such ores were found to be reducible to a new metal (the first discovered since ancient times), and this was ultimately named for the kobold.

Today, some cobalt is produced specifically from various metallic-lustered ores, for example cobaltite (CoAsS), but the main source of the element is as a by-product of copper and nickel mining. The copper belt in the Democratic Republic of the Congo, Central African Republic and Zambia yields most of the cobalt mined worldwide.

Michael Jones

Michael Jones or Mike Jones may refer to:

Athletes

Baseball

Association football

PTC

PTC may refer to:

In education:

In U.S. Healthcare

In organizations:

Thermistor

A thermistor is a type of resistor whose resistance is dependent on temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor. Thermistors are widely used as inrush current limiter, temperature sensors (NTC type typically), self-resetting overcurrent protectors, and self-regulating heating elements.

Thermistors differ from resistance temperature detectors (RTDs) in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals. The temperature response is also different; RTDs are useful over larger temperature ranges, while thermistors typically achieve a greater precision within a limited temperature range, typically −90 °C to 130 °C.

Basic operation

Assuming, as a first-order approximation, that the relationship between resistance and temperature is linear, then:

where

Thermistors can be classified into two types, depending on the classification of . If is positive, the resistance increases with increasing temperature, and the device is called a positive temperature coefficient (PTC) thermistor, or posistor. If is negative, the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient (NTC) thermistor. Resistors that are not thermistors are designed to have a as close to 0 as possible, so that their resistance remains nearly constant over a wide temperature range.

Auto racing

Auto racing (also known as car racing, motor racing or automobile racing) is a sport involving the racing of automobiles for competition. The main aim of an individual event is to set the fastest time in a set number of laps or time limit. The finishing order is determined by race time, with the fastest time in first place, second-fastest in second place and so on. Any driver failing to complete a race for any reason is deemed "retired", or, more commonly, "out". Retired drivers will have their positions determined by the order in which those retired, with the first to retire finishing last, the next second-last and so on. In most events, a driver's final race position may be classified if he/she completes a certain amount of the race distance, usually just short of completing the full race (for example, in Formula One, a driver's race position is classified if he/she completes 90% of the full race distance). There are numerous different categories of auto racing, each with different rules and regulations, such as compulsory pit stops and car regulations, for all cars and drivers to comply. The continuous exposure of a driver to vibration and G forces in years of automobile racing may have a substantial effect on the high incidence of musculoskeletal disorders.