Although designs and construction vary between brands, basic components of all ballpoint pens are universal. Standard components include the freely rotating ball point itself (distributing the ink), a socket holding the ball in place, and a self-contained ink reservoir supplying ink to the ball. In modern disposable pens, narrow plastic tubes contain the ink, which is compelled downward to the ball by gravity. Brass, steel, or tungsten carbide are used to manufacture the ball bearing-like points, then housed in a brass socket.
The function of these components can be compared with the ball-applicator of roll-on antiperspirant; the same technology at a larger scale. The ball point delivers the ink to the writing surface while acting as a buffer between the ink in the reservoir and the air outside, preventing the quick-drying ink from drying inside the reservoir. Modern ballpoints are said to have a two-year shelf life, on average.
The common ballpoint pen is a product of mass production, with components produced separately on assembly lines. Basic steps in the manufacturing process include production of ink formulas, moulding of metal and plastic components, and assembly. Marcel Bich was involved in developing the production of inexpensive ballpoint pens.
It starts with the raw clay, preferably in a mix with 2530% sand to reduce shrinkage. The clay is first ground and mixed with water to the desired consistency. The clay is then pressed into steel moulds with a hydraulic press. The shaped clay is then fired ("burned") at 9001000 C to achieve strength.
Starting in the 20th century, the use of brickwork declined in some areas due to concerns with earthquakes. Earthquakes such as the San Francisco earthquake of 1906 and the 1933 Long Beach earthquake revealed the weaknesses of unreinforced brick masonry in earthquake-prone areas. During seismic events, the mortar cracks and crumbles, and the bricks are no longer held together. Brick masonry with steel reinforcement, which helps hold the masonry together during earthquakes, was used to replace many of the unreinforced masonry buildings. Retrofitting older unreinforced masonry structures has been mandated in many jurisdictions.
Jim Dawson, Rock Around the Clock: The Record That Started the Rock Revolution! (San Francisco: Backbeat Books, 2005)
John W. Haley and John von Holle, Sound and Glory (Wilmington, DE: Dyne-American, 1990)
John Swenson, Bill Haley (London: W.H. Allen, 1982)
The causes of bipolar disorder likely vary between individuals and the exact mechanism underlying the disorder remains unclear. Genetic influences are believed to account for 6080 percent of the risk of developing the disorder indicating a strong hereditary component. The overall heritability of the bipolar spectrum has been estimated at 0.71. Twin studies have been limited by relatively small sample sizes but have indicated a substantial genetic contribution, as well as environmental influence. For bipolar disorder type I, the (probandwise) concordance rates in modern studies have been consistently estimated at around 40 percent in identical twins (same genes), compared to about 5 percent in fraternal twins. A combination of bipolar I, II and cyclothymia produced concordance rates of 42 percent vs. 11 percent, with a relatively lower ratio for bipolar II that likely reflects heterogeneity. There is overlap with unipolar depression and if this is also counted in the co-twin the concordance with bipolar disorder rises to 67 percent in monozygotic twins and 19 percent in dizygotic. The relatively low concordance between dizygotic twins brought up together suggests that shared family environmental effects are limited, although the ability to detect them has been limited by small sample sizes.