More recently, the term has also been applied to the chronometer watch, a watch that meets precision standards set by the Swiss agency COSC. The most accurate timekeeping devices are atomic clocks, which are accurate to seconds in many millions of years, and are used to calibrate other clocks and timekeeping instruments. Atomic clocks use the frequency of electronic transitions in certain atoms to measure the second. One of the atoms used is caesium, most modern atomic clocks probe caesium with microwaves to determine the frequency of these electron vibrations. Since 1967, the International System of Measurements bases its unit of time, the second, on the properties of caesium atoms. SI defines the second as 9,192,631,770 cycles of the radiation that corresponds to the transition between two electron spin energy levels of the ground state of the 133Cs atom. Today, the Global Positioning System in coordination with the Network Time Protocol can be used to synchronize timekeeping systems across the globe. In medieval philosophical writings, the atom was a unit of time referred to as the smallest possible division of time. The earliest known occurrence in English is in Byrhtferths Enchiridion (a science text) of 1010–1012, where it was defined as 1/564 of a momentum (11⁄2 minutes), and thus equal to 15/94 of a second. It was used in the computus, the process of calculating the date of Easter.
Clonorchis sinensis and Opisthorchis viverrini are both categorized by the International Agency for Research on Cancer (IARC) as Group 1 carcinogens.In humans, the onset of cholangiocarcinoma occurs with chronic opisthorchiasis, associated with hepatobiliary damage, inflammation, periductal fibrosis and/or cellular responses to antigens from the infecting fluke. These conditions predispose to cholangiocarcinoma, possibly through an enhanced susceptibility of DNA to damage by carcinogens. Chronic hepatobiliary damage is reported to be multi-factorial and considered to arise from a continued mechanical irritation of the epithelium by the flukes present, particularly via their suckers, metabolites and excreted/secreted antigens as well as immunopathological processes. In silico analyses using techniques of genomics and bioinformatics is unraveling information on molecular mechanisms that may be relevant to the development of cholangiocarcinoma.In regions where Opisthorchis viverrini is highly endemic, the incidence of cholangiocarcinoma is unprecedented. For instance, cholangiocarcinoma represents 15% of primary liver cancer worldwide, but in Thailands Khon Kaen province, this figure escalates to 90%, the highest recorded incidence of this cancer in the world. Of all cancers recorded worldwide in 2002, 0.02% were cholangiocarcinoma caused by Opisthorchis viverrini. Cancer of the bile ducts caused by opisthorchiasis occurs in the ages 25–44 years in Thailand. A few cases have appeared in later life among U.S. veterans of the Vietnam War, who consumed poorly cooked fish from streams in endemic areas near the border of Laos and Vietnam. Diagnosis
The medical diagnosis is usually established by finding eggs of Opisthorchis viverrini in feces using the Kato technique.