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Movements, leaders, victories and the continuing fight for equality.
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Explore the people, places, events, achievements, struggles and stories that shaped our journey.
Movements, leaders, victories and the continuing fight for equality.
Innovation, patents, science, technology and world-changing contributions.
Pioneers, champions, Negro Leagues, records, activism and excellence.
Meet the people whose lives, choices and achievements shaped the journey.
Black towns, communities, institutions and places where history happened.
Moments that changed communities, movements, institutions and the nation.
In 1968 Shirley Chisholm became the first Black woman elected to the United States Congress. In 1972 she launched a campaign for the Democratic presidential nomination, breaking another political barrier.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
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| IUPAC name
2-Hydroxyethyl 2-methylprop-2-enoate--ethane-1,2-diyl bis(2-methylprop-2-enoate)
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CompTox Dashboard (EPA)
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Polymacon is a non-proprietary (i.e., generic) term for a hydrophilic polymer of 2-hydroxyethylmethacrylate (HEMA) cross-linked with ethylene glycol dimethacrylate (62%) and water (38%).[1] It is used in the manufacture of soft contact lenses, and is considered a low-hydration hydrogel of nonionic polymer.[2]
 | This article about polymer science is a stub. You can help Wikipedia by adding missing information. |
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
Polymacon is a non-proprietary (i.e., generic) term for a hydrophilic polymer of 2-hydroxyethylmethacrylate (HEMA) cross-linked with ethylene glycol dimethacrylate (62%) and water (38%). It is used in the manufacture of soft contact lenses, and is considered a low-hydration hydrogel of nonionic polymer.
Oxygen permeability (OP) is a parameter of a contact lens that expresses the ability of the lens to let oxygen reach the eye by diffusion. In soft contact lenses, it is dependent on the thickness of the lens and the material of the lens, especially concerning the water content. Because of this dependence on thickness, transmissibility level (abbreviated Dk/t), the Dk per thickness of the lens, is more commonly used. The earliest models of soft contact lenses, based on hydrogel material, had a level of oxygen permeability of around 6–8 Dk/t. Polymacon, the material used in the first hydrogel contact lenses in some countries in the 1960s and approved by the FDA in the U.S. in 1971, has a Dk of 9 . These days, typical values of oxygen permeability for hydrogel contact lenses range from 25 to 50. For example, Nelfilcon A has a Dk value of 26, and the Omafilcon A has a Dk of 25. While those numbers are typical of hydrogel contact lenses, many contact lenses are made of silicone hydrogel, which has a much higher oxygen permeability. For example, the Dk value of Lotrafilcon B and Comfilcon A, two silicone hydrogels, is 110 and 128, respectively. These values are more than twice the values of oxygen permeability for hydrogel materials. D being diffusivity (cm2/sec) – a measure of how fast the oxygen moves through the material. Note, different sources may use different units: contact package inserts often use cm2/sec, while academic papers may use other values for distance such as mm2/sec. k being the solubility (ml O2/ml of material × mm Hg) – a measure of how much oxygen is contained in the material. Once again, various sources may use units of different sizes. Do not assume that they're the same unless specified by the source.
Benzalkonium chloride (BZK, BKC, BAK, BAC), also known as alkyldimethylbenzylammonium chloride (ADBAC) is a type of cationic surfactant. It is an organic salt classified as a quaternary ammonium compound. ADBACs have three main categories of use: as a biocide, a cationic surfactant, and a phase transfer agent. ADBACs are a mixture of alkylbenzyldimethylammonium chlorides, in which the alkyl group has various even-numbered alkyl chain lengths.
A hydrogel is a biphasic material, a mixture of porous and permeable solids and at least 10% of water or other interstitial fluid. The solid phase is a water insoluble three dimensional network of polymers, having absorbed a large amount of water or biological fluids. Hydrogels have several applications, especially in the biomedical area, such as in hydrogel dressing. Many hydrogels are synthetic, but some are derived from natural materials. The term "hydrogel" was coined in 1894.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Madam C.J. Walker
