The origin of the security gate: the earliest security gate in the history of our country

The origin of security gates: It is hard to imagine the earliest security gates in the history of our country. The earliest security gates were traced back to the Qin Dynasty more than 2,000 years ago.

The earliest established security inspection gate in China was the "Magnetic Gate" set on the northern Tuen Mun Gate of the Qin Shihuang Period and the Afang Palace. It has a history of more than 2,200 years.
In the thirty-five years of Emperor Qin Shihuang, the Emperor ordered the re-construction of a new palace on the south bank of the Weihe River. In order to prevent problems, the Emperor ordered the craftsmen to consider safety issues when building a new palace. According to the original intention of the Emperor, the craftsmen used the scientific principle that the magnetic magnetism that people had known at the time had attracted or rejected the metal. After repeated experiments, they finally decided to use the Afang Palace for the "four Yishang people", that is, for foreigners. The north gate was made of magnets. If someone secretly carries weapons through the magnet door into the palace, the powerful magnetic field generated by the magnetized door frame will immediately exert a strong attraction or repulsive force on his weapon, thus discovering whether the person entering the door has hidden weapons.

With the continuous occurrence of various terrorist attacks around the world, public security has received increasing attention from all countries. China is rapidly developing the subway. By 2015, the operating mileage will increase from the current 1,000 kilometers to more than 4,000 kilometers. The development of the subway has brought convenience to people. At the same time, there are hidden threats and risks. Strengthening the security measures of the subway is an important part of preventing terrorist attacks. It is also one of the links that the current technical means need to be upgraded. The subway security inspection includes the detection of the human body itself and the personal belongings. The purpose of the inspection is to discover hidden weapons, explosives, radioactive materials and even biochemical agents that may be used for terrorist activities.

Mono Calcium Phosphate ,the chemical formula is  Ca (H2PO4)2.H2O, molecular weight of the body is 252.06, after dryed the product is white or slightly yellow micro powder or granules, the relative density of 2.22 (16 Â°C). Slightly hygroscopic, soluble in hydrochloric acid, nitric acid, slightly soluble in cold water, almost insoluble in ethanol. At 30 Â°C, 100 ml of water soluble MCP 1.8g. The aqueous solution was acidic, heating the aqueous solution can get calcium hydrogen phosphate. Lose crystal water at 109 Â°C and decomposed into calcium metaphosphate at 203°C. Applications:Monocalcium Phosphate is used to supply mineral nutrition such as phosphorus (P) and calcium (Ca) for animal, which can be easily digested and absorbed. Extensively applied as additives of Phosphorous and Calcium in aquatic animals feed.Higher water solubility of MCP is required in aquatic animals feed.

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