Human immunodeficiency virus (HIV) infects and destroys T cells. Without the key defence that these T cells provide, the body becomes prone to infections that otherwise would not affect healthy people.
The extent of HIV progression is found by measuring the percentage of CD4 T cells in the patient's blood. The effects of other virus or lymphocyte disorders can also often be estimated by counting the numbers of lymphocytes present in the blood.
Author
An author is a person who writes books, stories, poems, or other written work. Their writing can be truth or fiction, short or long. Often, "author" is a word for a professional writer, but any person who writes may also be called that.
Sometimes, a person who creates something that is not prose is called an author. Someone who writes music may be called the author of that piece of music, though we would usually call that person a composer. In the film world, the French word for author, "auteur", is often used about someone who has been both the writer and director of a movie.
In biology, the first person to write an article that gives a name to and describes a type of living thing is the author of that name.
In copyright law, the author is the first owner of copyright. Such laws also apply to other works of art such as pictures or music.
Pedipalp
Pedipalps are the two appendages on the front of a spider's head. Some spiders seem to have ten legs and not eight, because these pedipalps look like an extra pair of legs. The pedipalps are used rather like arms. Spiders often use them to hold insects (for example crickets) for them to eat.
Male spiders also use pedipalps for mating. The male spiders make some silk, put sperm onto the silk, and then put their pedipalps into the sperm. The pedipalps then hold the sperm, and the spider can use it to mate with a female by putting them inside her epigynum.
The pedipalps of all chelicerates vary: Ricinulei, Thelyphonida, Amblypygi, some Opiliones, Schizomida, Scorpions and pseudoscorpions all have theirs as pincers, with the Amblypygi's being their entire pedipalps shaped like mantids. The Palpigradi's pedipalps have some of the strangest roles of arachnids as they use theirs for locomotion. The pedipalps of Solifugae act as antenna.
Ionic compound
In chemistry, an ionic compound is a compound made of ions. They have strong ionic bonds between particles. Lots of energy (heat) is required to break the bond apart, resulting in high melting and boiling points. The ions join together because they have different charges. Compounds of metals and non-metals are usually ionic. They are made when two or more atoms come close together and an electron goes from one atom to the other atom. The electron does this because both atoms want a full outer shell, similar to those of the noble gases.
Note 1: carbon and silicon in Group 4 usually form covalent bonds by sharing electrons.
Note 2: the elements in Group 0 do not react with other elements to form ions.
ELISA
The ELISA method (Enzyme Linked Immuno-Sorbent Assay) is a technique used in biochemistry to determine if a certain substance--such as a specific cytokine or antigen--is present within a sample. It is sometimes abbreviated as "EIA."
This technique uses special antibodies that attach themselves to the substance. These antibodies generate a specific color. The amount of color indicates the amount of substance present. (Sometimes, the substance must be viewed under ultraviolet light for the antibodies to generate this color.)
Another set of antibodies are used to "capture" the substance. These antibodies adhere to both the substance and the testing container, thus holding the substance in place.
A more sophisticated and sensitive technique, the ELISPOT method, was derived from the ELISA techique.
David Hume
David Hume (7 May 1711 – 25 August 1776) was a philosopher and historian from Scotland. When he was still alive, people thought of him as a historian. He wrote a series of large books called "The History of England". But today, people think of Hume as an important philosopher.
In his books on philosophy, Hume said that many of our beliefs do not come from reason. Instead, they come from our instincts or feelings. For example, reason does not tell us that one thing causes another. Instead, we see one thing and then we see another, and we "feel" a link between the two. Similarly, reason does not tell us that someone is a good person. Instead, we see that the person is kind and friendly, and we "feel" a special moral feeling. Because Hume thought that these beliefs do not come from reason, people call him a "skeptical" or "anti-rationalist" philosopher.
Hume is famous for his 'Induction Fallacy'. This draws attention to a common mistake people make. People see something, and make claims that what they see will always be as they see it. For example, people see only white swans and claim that all swans are white. This is 'fallacious' or mistaken, because it is always possible that they then will see a black swan.
Hume was also skeptical about religion. He was not a religious person and religious people did not like his opinions. He did not believe in miracles. He said that suicide wasn't always wrong, but never said whether or not he believed in God. In 1776, when he was dying, his friends found him very calm about death, despite him not believing in an Afterlife. Today, Hume's books are very important to philosophers who are interested in religion.
Today's philosophers sometimes use the term 'Hume's fork' to refer to Hume calling everything we can think about either a relation of ideas (things like mathematics, that must be true) or a matter of fact (like science, where we have to look at things to tell whether or not they are true).
Another philosopher, Immanuel Kant, read some of Hume's books and changed his mind about some important things. Kant said Hume had made him wake up from a sleeping dogmatism, the traditional metaphysics.
Here are Hume's most important books:
Bath
A bath (UK English) or bathtub (US English) is a basin large enough for people sit in when washing their body. The bath is usually in the bathroom. A less common name for a bath is a "washtub".
Sometimes people will add scents, oils and salts to the bath for better experience.
A bath is also a place where people can sit in water (or other liquids, often hot) for their health. This is where the town name Bath comes from. Public baths for relaxing were built in all parts of the Roman Empire.
Brush
A brush is a tool with bristles or wires or other filaments sticking out. There are many kinds. Most brushes have a long part at one end to hold (the handle), on the other end from the head that carries the bristles or filaments. We use brushes for cleaning, making hair look good, painting, and other purposes.
Many kinds of brushes are made for cleaning, for example toothbrushes or brushes for cleaning floors.
We use paint brushes for putting ink or paint on paper. Computer graphics uses digital paintbrushes for making pictures
Paint brushes can have three shapes:
We can buy brushes in different sizes and materials. Here are some sorts.
The sizes of brushes used for painting and decorating (changing the colour or look of a room) are usually in millimeters or inches. This shows how wide the head is.
Here are some sizes:
We can buy brushes with natural or synthetic (man-made) bristles. Handles (the part of the brush we hold) may be wood or plastic.
Artists' brushes usually have sizes with numbers, but there is no standard.
From smallest to largest, the sizes are:
We use sizes "000" to "20" most often.
Bristles may be natural -- either soft hair or hog (pig) bristle -- or synthetic (man-made).
Artists' brush handles (the part of the brush we hold) are often wooden, but the cheapest brushes may have plastic handles. Many cheap handles are made of unfinished wood; better quality handles are of finished wood.
Starch