As of May 2010, the smallest time interval uncertainty in direct measurements is on the order of 12 attoseconds (1.2 × 10−17 seconds), about 3.7 × 1026 Planck times. Units
The second (s) is the SI base unit. A minute (min) is 60 seconds in length, and an hour is 60 minutes or 3600 seconds in length. A day is usually 24 hours or 86,400 seconds in length; however, the duration of a calendar day can vary due to Daylight saving time and Leap seconds. Definitions and standards
A time standard is a specification for measuring time: assigning a number or calendar date to an instant (point in time), quantifying the duration of a time interval, and establishing a chronology (ordering of events). In modern times, several time specifications have been officially recognized as standards, where formerly they were matters of custom and practice. The invention in 1955 of the caesium atomic clock has led to the replacement of older and purely astronomical time standards such as sidereal time and ephemeris time, for most practical purposes, by newer time standards based wholly or partly on atomic time using the SI second. International Atomic Time (TAI) is the primary international time standard from which other time standards are calculated. Universal Time (UT1) is mean solar time at 0° longitude, computed from astronomical observations. It varies from TAI because of the irregularities in Earths rotation. Coordinated Universal Time (UTC) is an atomic time scale designed to approximate Universal Time. UTC differs from TAI by an integral number of seconds.
A literature review found two cases of copper deficiency myelopathy secondary to parenteral zinc supplementation during chronic dialysis.Metallic zinc is the core of all United States currency coins, including copper-coated pennies. People who ingest a large number of coins will have elevated zinc levels, leading to zinc-toxicity-induced copper deficiency and the associated neurological symptoms. This was the case for a 57-year-old woman diagnosed with schizophrenia. The woman consumed over 600 coins, and started to show neurological symptoms such as unsteady gait and mild ataxia. Hereditary disorders
Menkes disease is a congenital disease that is a cause of copper deficiency. Menkes disease is a hereditary condition caused by a defective gene involved with the metabolism of copper in the body. Menkes disease involves a wide variety of symptoms including floppy muscle tone, seizures, abnormally low temperatures, and a peculiar steel color hair that feels very rough. Menkes disease is usually a fatal disease with most children dying within the first ten years of life. Other
It is rarely suggested that excess iron supplementation causes copper deficiency myelopathy. Another rarer cause of copper deficiency is celiac disease, probably due to malabsorption in the intestines. Still, a large percentage, around 20%, of cases have unknown causes. Pathophysiology
Copper functions as a prosthetic group, which permits electron transfers in key enzymatic pathways like the electron transport chain. Copper is integrated in the enzymes cytochrome c oxidase, which is involved in cellular respiration and oxidative phosphorylation, Cu/Zn dismutase, which is involved in antioxidant defense, and many more listed in the table below.