In the 20th century, composers have continued to write string quartets. Claude Debussy (1862-1918) and Maurice Ravel (1875-1934) each wrote one. Arnold Schoenberg even added a voice to his first String Quartet. Béla Bartók (1881-1945) wrote six string quartets which are very hard to play. They have very exciting rhythms which often come from his native Hungarian folk music, as well as complex harmonies. Dmitri Shostakovich (1906-1975) wrote fifteen and Benjamin Britten (1913-1976) wrote three.
Playing in a string quartet is highly enjoyable. There are many great works by famous composers, as well as some music which has been written for young players who are learning.
There are professional players who form string quartets and who play together for many years. In the early part of the 20th century the Rosé Quartet was thought by many to be the best in Europe. Later the Amadeus Quartet became very famous.
Opus number
Opus or the shortened form op. after the title of a piece of music means “work”. It is followed by a number. When a composer writes their first piece of music it is followed by the term “opus 1”. The next composition would then be called “opus 2”, etc.
Giving pieces of music opus numbers helps us to identify which piece of music (from a certain composer) that composition is. For example: Beethoven wrote lots of piano sonatas. His first Piano sonata in A flat major has the opus number of op.26. This shows that he wrote this sonata when he was young in his composing career. Many years later, he wrote another piano sonata which is also in A flat major, and this piece one has the opus number of 110 (op. 110).
You cannot always tell from a composer’s opus numbers the order in which the works were composed. Until around the end of the 18th century, opus numbers were only given to pieces of music which were published.
Some musicologists (people who study and write about music) have studied all the works by a famous composer and have given them a catalogue number. For example Mozart’s music does not have opus numbers. Some of them are long operas, others are tiny little pieces for the piano he might have written in a hurry one day. A man called Köchel made a list of every single work by Mozart and gave them K numbers (K for Köchel). His numbering goes up to 622. This is useful, for example, to tell the difference between his Symphony in G minor K183 and his Symphony in G minor K550.
The plural of “opus” is “opuses” in English. This is because the Latin plural is opera which is rather confusing to English speakers as the word is already used in musical terminology.
The word "opus" can also refer to the "work" of an artist. (For example: "This opus was composed by Chopin," or "This opus is the last Piano sonata that Beethoven composed")
An artist's "magnum opus" means his or her "greatest" work.
Amino acid
Amino acids are the building blocks of proteins. In eukaryotes, there are 20 standard amino acids out of which almost all proteins are made.
In biochemistry, an amino acid is any molecule that has both amine (NH+R) and carboxyl (C=O) functional groups. In biochemistry, this term refers to alpha-amino acids with the general formula HNCHRCOOH, where R is one of many side groups (see diagram).
About 500 amino acids are known. For animals, the most important thing that amino acids do is to make proteins, which are very long chains of amino acids. Every protein has its own sequence of amino acids, and that sequence makes the protein take different shapes, and have different functions. Amino acids are like the alphabet for proteins; even though you only have a few letters, if you connect them, you can make many different sentences.
Nine of the 20 standard amino acids are "essential" amino acids for humans. They cannot be built (synthesised) from other compounds by the human body, and so must be taken in as food. Others may be essential for some ages or medical conditions. Essential amino acids may also differ between species. Herbivores have to get their essential amino acids from their diet, which for some is almost entirely grass. Ruminants such as cows get some amino acids via microbes in the first two stomach chambers.
An amino acid is an organic chemical. It consists of an α-carbon atom that is covalently bonded to four groups.
Every amino acid has at least one amino group (-NH) and one carboxyl group (-COOH), except proline.
These are the proteinogenic amino acids, which are the building blocks for proteins. They are produced by cellular machinery coded for in the genetic code of any organism.
† The stop codon is not an amino acid, but is included for completeness.
†† UAG and UGA do not always act as stop codons (see above).
‡ An essential amino acid cannot be synthesized in humans. It must be supplied in the diet. Conditionally essential amino acids are not normally required in the diet, but must be supplied to populations which do not make enough of it.
To these α-amino acids further in biosynthesis processes appearing non-essential ones are structurally (here by using SMILES notation) related:
OC(=O)C(N)–
Enlightenment
Enlightenment has several meanings. Some of them are given below:
Miscarriage
A miscarriage is the natural death of an embryo or fetus in the womb, before it is old enough to live on its own, outside the mother. The medical words for a miscarriage are spontaneous abortion. ("Spontaneous" means something that a person did not expect to happen. An "abortion" is when a pregnancy ends early, before birth.)
Among women who know they are pregnant, about 15-20% have miscarriages. (This means that up to 1 in every 5 women who know they are pregnant miscarries.) It is the most common complication (serious problem) that happens in early pregnancy in humans.
In the United States, if a fetus dies after it is 20 weeks old, its death is no longer called a miscarriage. Its death is called a "stillbirth", a "fetal demise", or a "fetal death". ("Demise" means "death.") Different countries have different ways of defining the difference between a miscarriage and a fetal death. For example:
Nobody knows all of the reasons why a woman may miscarry. However, some common causes include:
The most common causes of miscarriage change depending on what trimester the mother is in. (Each trimester lasts about three months.)
Most miscarriages happen during the first trimester. Some studies say that two-thirds (two out of three) to three-quarters (three out of four) of all miscarriages happen during this trimester. About 30% to 40% (3 to 4 in every 10) of all fertilized eggs miscarry, often before a woman knows she is pregnant.
In more than half of embryos miscarried in the first 13 weeks of pregnancy, the embryo has chromosomes that are not normal. These chromosomal problems may happen because of problems as the embryo grows and its cells make copies of themselves. It is also possible for chromosomal problems to happen because of a problem with a parent's genes. However, this is more likely to happen in women who have had other miscarriages, or if one of the parents has a child or other relatives with birth defects. Genetic problems are more likely to happen with older parents; this may be why miscarriages are more common in older women.
Another cause may be the mother not having enough progesterone. If a woman is diagnosed with low progesterone levels in the second half of her menstrual cycle (the luteal phase), she may be prescribed progesterone, to take during the first trimester of her pregnancy. However, when a woman might already be miscarrying, there is no evidence that first-trimester progesterone pills decrease the risk of having a miscarriage. Scientists have even questioned whether problems with the luteal phase really can cause miscarriages.
Common causes of miscarriage during the second trimester are: