Patellofemoral pain syndrome (PFPS; not to be confused with jumpers knee) is knee pain as a result of problems between the kneecap and the femur. The pain is generally in the front of the knee and comes on gradually. Pain may worsen with sitting, excessive use, or climbing and descending stairs.While the exact cause is unclear, it is believed to be due to overuse. Risk factors include trauma, increased training, and a weak quadriceps muscle. It is particularly common among runners. The diagnosis is generally based on the symptoms and examination. If pushing the kneecap into the femur increases the pain, the diagnosis is more likely.Treatment typically involves rest and rehabilitation with a Physical Therapist. Runners may need to switch to activities such as cycling or swimming. Insoles may help some people. Symptoms may last for years despite treatment. Patellofemoral pain syndrome is the most common cause of knee pain, affecting more than 20% of young adults. It occurs about 2.5 times more often in females than males. Signs and symptoms
The onset of the condition is usually gradual, although some cases may appear suddenly following trauma. The most common symptom is diffuse vague pain around the kneecap (peripatellar) and localized pain focused behind the kneecap (retropatellar). Affected individuals typically have difficulty describing the location of the pain. They may place their hands over the anterior patella or describe a circle around the patella. This is often called the "circle sign".
The explosive power of nitroglycerin derives from detonation: energy from the initial decomposition causes a strong pressure wave that detonates the surrounding fuel. This is a self-sustained shock wave that propagates through the explosive medium at 30 times the speed of sound as a near-instantaneous pressure-induced decomposition of the fuel into a white-hot gas. Detonation of nitroglycerin generates gases that would occupy more than 1,200 times the original volume at ordinary room temperature and pressure. The heat liberated raises the temperature to about 5,000 °C (9,000 °F). This is entirely different from deflagration, which depends solely upon available fuel regardless of pressure or shock. The decomposition results in a much higher ratio of energy to gas moles released compared to other explosives, making it one of the hottest detonating high explosives. Manufacturing
Nitroglycerin can be produced by acid-catalyzed nitration of glycerol (glycerin). The industrial manufacturing process often reacts glycerol with a nearly 1:1 mixture of concentrated sulfuric acid and concentrated nitric acid. This can be produced by mixing white fuming nitric acid—a quite expensive pure nitric acid in which the oxides of nitrogen have been removed, as opposed to red fuming nitric acid, which contains nitrogen oxides—and concentrated sulfuric acid. More often, this mixture is attained by the cheaper method of mixing fuming sulfuric acid, also known as oleum—sulfuric acid containing excess sulfur trioxide—and azeotropic nitric acid (consisting of about 70% nitric acid, with the rest being water). The sulfuric acid produces protonated nitric acid species, which are attacked by glycerols nucleophilic oxygen atoms.