The study of liquid crystals began in 1888 when an Austrian botanist named Friedrich Reinitzer observed that a material known as cholesteryl benzoate had two distinct melting points. In his experiments, Reinitialize increased the temperature of a solid sample and watched the crystal change into a hazy liquid. As he increased the temperature further, the material changed again into a clear, transparent liquid. Because of this early work, Reinitzer is often credited with discovering a new phase of matter - the liquid crystal phase. Liquid crystal materials are unique in their properties and uses. As research into this field continues and as new applications are developed, liquid crystals will play an important role in modern technology. This tutorial provides an introduction to the science and applications of these materials.
Aerosols are known as pressurized packages, which us liquified propellants. These are convenient and easy to use. Medication is dispensed in a ready-to-use form on pressing a button
Aerosol is defined as a dispersion system that functions on the power of compressed or liquified gas to expel the contents from the container.
On 10th April 1901, Dr. Duncan "om" MacDougall conducted an unusual experiment to prove that humans have soul. According to MacDougall if soul is consider as Matter & it is present in human body then it must have some mass. To calculate mass of soul Dr.MacDougall have to measure weight of human body before & after death.
To measure accurate weight macdougall made a custom weight measure machine on which he
Ordinary reactions occur by absorption of heat energy from outside. The reacting molecules are energised and molecular collisions become effective. These bring about the reaction. The reactions which are caused by heat and in absence of light are called thermal or dark reactions. On the other hand, some reactions proceed by absorption of light radiations. These belong to the visible and ultraviolet regions of the electromagnetic spectrum (2000 to 8000 Å). The reactant molecules absorbs photons of light and get excited. These excited molecules then produce the reactions. A reaction which takes place by absorption of the visible and ultraviolet radiations is called a photochemical reaction. The branch of chemistry which deals with the study of photochemical reactions is called photochemistry.
Cells are the basic units of tissues, which form organs and systems in the human body. Traditionally, body cells are divided in to two main types: epithelial and mesenchymal cells. In health, the cells remain in accord with each other. In 1859, Virchow first published cellular theory of disease, bringing in the concept that diseases occur due to abnormalities at the level of cells. Since then, study of abnormalities in structure and function of cells in disease has remained the focus of attention in understanding of diseases. Thus, most forms of diseases begin with cell injury followed by consequent loss of cellular function. Cell injury is defined as a variety of stresses a cell encounters as a result of changes in its internal and external environment. In general, cells of the body have inbuilt mechanism to deal with changes in environment to an extent.
A nuclear reaction is different from a chemical reaction. In a chemical reaction, atoms of the reactants combine by a rearrangement of extranuclear electrons but the nuclei of the atoms remain unchanged. In a nuclear reaction, on the
other hand, it is the nucleus of the atom which is involved. The number of protons or neutrons in the nucleus changes to form a new element. A study of the nuclear changes in atoms is termed Nuclear Chemistry.