الأربعاء، 4 مايو 2016

Encyclopedia:Physics

Encyclopedia:Physics



Newly published articles in physics

  • Tanmay Vachaspati, Levon Pogosian, Danièle A Steer (2015) Cosmic strings Scholarpedia, 10(2):31682.

Citric acid

Citric acid


Citric acid is a weak organic tribasic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms.
More than a million tons of citric acid are manufactured every year. It is used widely as an acidifier, as a flavoring, and as a chelating agent.[8]
A citrate is a derivative of citric acid; that is, the saltsesters, and the polyatomic anion found in solution. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate. When part of a salt, the formula of the citrate ion is written as C6H5O73− or C3H5O(COO)33−.

حمض النتريك

حمض النتريك




حمض النيتريك أو حمض الآزوت أو ماء النار[1] أو ماء الفضة[2] (كما سماه جابر بن حيانHNO3 هو حمض معدنى قوي، شديد التآكلية، سام، له القدرة على إحداث حروق خطيرة عديم اللون في حالة نقاوته، العينات القديمة يميل لونها إلى الأصفر نتيجة تراكم أكاسيد النيتروجين. إذا كان المحلول يحتوى على أكثر من 86% حمض نيتريك، فإنه يسمى بحمض النيتريك المدخن، حمض النيتريك المدخن يميز كحمض النيتريك المدخن الأبيض وحمض النيتريك المدخن الأحمر على حسب كمية ثاني أكسيد النيتروجين المحتوى عليها.

فن الحوار والاقناع - ماهي المهارات التي يجب ان تتعلمها لتكون متحدث ماهر عن جد

الفينول

الفينول



الفينول هو مركب صلب بلوري عديم اللون ذو رائحة قاريّة لطيفة، وغالبًا ما يشار إليها برائحة المشافيصيغته الكيميائية المجملة C6H6O، والتي يمكن أن تكتب بالشكل المفصل C6H5OH. وبنيته عبارة عن زمرة الهيدروكسيل مرتبطة بحلقة فينيل، وبالتالي فهو مركب عطري.

مهارة الحلقة 6 | مهارة الإلقاء 1 | الإعداد والتحضير | مؤسسة نيو ميديا

Famous chemists ...




Chemistry is a study of reactions between chemicals and substances that most people experience in their everday life. All of our medicines and household products are the result of a history of chemical studies and discoveries. Below is a list of some of the most important chemists of all time organized by the significance of their contributions to this field.
marie-curieMarie Curie (1867–1934)
Famous For: Discovery of Radium and Polonium
Marie Curie received the Nobel Prize in Chemistry in 1911 for her discovery of radium and polonium. She was able to isolate and study the compounds and nature of radium.
Tableau_Louis_PasteurLouis Pasteur (1822–1895)
Famous For: The process of Pasteurization and creation of Vaccines for Rabies and Anthrax
In addition to developing the process of Pasteurization, Louis Pasteur discovered the assymetrical molecular structure on certain crytals. He made some of the earliest vaccines for rabies and anthrax, and the reduction of a bacterial infection in what is known as puerperal fever.
John_DaltonJohn Dalton (1766–1844)
Famous For: Identification and presenting the atomic theory
Recognized for his work on the atomic theory and research on color blindness. He successfully identified chemical compounds and reactions affected by interaction of atoms with one another.
George_Washington_CarverGeorge Washington Carver (1864–1943)
Famous For: Promoting alternative crops to cotton, such as peanuts, soybeans, sweet potatoes
George Washington Carver found different crops to use instead of cotton. He used peanuts, soybeans, sweet potatoes to keep the land productive. His intention was to keep the poor farmers healthy and productive.
Faraday_CochranMichael Faraday (1791–1867)
Famous For: His contributions in electrochemistry and electromagnetism
Faraday’s extensive work in the field of Chemistry includes the study chloring and carbon, both of which he discovered. In addition he made the earliest type of what we know today as the Bunsen burner. He was the first to identify would known as nanoparticles in mettalic form.
alfredAlfred Nobel (1833–1896)
Famous For: Inventing the dynamite
As the inventor of the dynamite, Alfred Nobel is seen as a chemist, innovator, engineer, and arms manufacturer. One of his earliest inventions include the gas meter. At one time, he held nearly 350 patents on various items.
Rosalind_FranklinRosalind Franklin (1920–1958)
Famous For: Discovery of the DNA structure in genetics
Rosalind Elsie Franklin and her contributions to science involve the study of the structures of coal, graphite, DNA, RNA, and viruses in understing their molecular structures.
antonie-lavoisierAntoine Lavoisier (1743–1794)
Famous For: Being the “Father of Modern Chemistry”
Lavoisier was able to show the relationship between oxygen and metal, resulting in rust. He also was able to show the role of oxygen in plant respiration and in animals. It was he who showed that water was made of hydrogen and oxygen, and that air was composed mainly of oxygen and nitrogen in its gaseous state.
BoyleRobert Boyle (1627–1691)
Famous For: Being the first “Modern Chemist”
Boyle was the one of the earliest men to apply the scientific method in chemistry and physics. His book, The Sceptical Chymyst, is considered a foundational source of literature on the field of chemistry.
linus-paulingLinus Pauling (1901–1994)
Famous For: His work in molecular biology and quantum chemistry
A recipient of the Nobel Prize in the field of chemistry in 1954. His work in the field of chemistry is chronicled in his book The Nature of the Chemical Bond is believed as one of the most foundational books on chemistry.
dmitri-mendeleevDmitri Mendeleev (1834–1907)
Famous For: Creating the table of elements used in chemistry and physics
In addition to the creation of the periodic table, Mendeleev work on the spectroscope and the capillarity of liquids, both of which continue to be used to this day. Politics got in the way of Dmitri from receiving the Nobel Prize in 1906.
joseph-priestleyJoseph Priestley (1733–1804)
Famous For: Inventing soda water
As a chemist, Joesph Priestly has been credited with the discovery of oxygen. He shares that distinction with Lavoisier and Scheele. More importantly, we have Priestly to thank for “soda water”, which he invented.
Mario-MolinaMario Molina (1943)
Famous For: Discovered the ozone hole in the Antarctic
As one of three recipients of the Nobel Prize in Chemistry in 1995, Molina co-discovered the harm that chlorofluorocarbons had on the ozone layer.
Humphry_DavyHumphry Davy (1778–1829)
Famous For: The discovery for earth based alkaline metals and alkali
Humphrey Davy’s contribution can be summarized in his discoveries on the nature of chlorine and iodine in its natural state. In addition, people remember for his identifying earth based alkaline metals and alkali itself.
fritz-haberFritz Haber (1868-1934)
Famous For: Being the “Father of Chemical Warfare” and synthesizing ammonia used in fertilizers and explosives
Recipient of the Nobel Prize in 1918, Haber was responsible for the development of the synthesizing process of ammonia. He has been referred to at times as the “Father or Chemical Warfare” in which he developed chlorine and poisonous gases during the Great War, WW I.
otto-hahnOtto Hahn (1879–1968)
Famous For: Being the “Father of Nuclear Chemistry”
Hahn was one of the earliest men to work in the field of radiochemistry and radioactivity. During one of his experiments, he founded what is known as “Applied Radiochemistry” which eventually led to nuclear chemistry.
Svante_ArrheniusSvante Arrhenius (1859-1927)
Famous For: Theory of the Greenhouse Effect and founder on the science of Physical Chemistry
Arrhenius advanced the theory to help explain the “ice age” which resulted in what is known as the “greenhouse effect.” He also provided the Arrhenius equation which is a formula to calculate reaction rates when the temperature is raised on certain chemicals.
ahmed-hassan-zewailAhmed Zewail (1946)
Famous For: Being the “Father of Femtochemistry”
Zewali was the first to delve into the field of “femtochemistry”, which is studying chemical reactions measured in femtoseconds (10 to -15 of a second). He received a Nobel Prize in 1995 for his advancement of the field of femtochemistry.
frederick-sangerFrederick Sanger (1918)
Famous For: Successful determination of base sequences in nucleic acids
The research work undertaken by Frederick Sanger involved his successful sequencing of DNA, insulin, and RNA. He was awarded the Nobel Prize two times, both for his work in chemistry, in 1958 and in 1980. He was able to establish a baseline in “the determination of base sequences in nuclein acids.”
Cannizzaro_StanislaoStanislao Cannizzaro (1826-1910)
Famous For: The Cannizzaro reaction
Cannizzaro worked extensively on organic chemistry in addition to his explanation which on how certain chemical reactions take place certain elements lact the hydrogen atom. This is named aptly as the Cannizaro reaction.
Graham_ThomasThomas Graham (1805-1869)
Famous For: His work on the diffusion of gases and the application of dialysis.
The discovery of Graham on the use of dialysis has its roots on his study of colloids. He was able to separate crystalloids from colloids using a dialyzer. His work on the diffusion of gases has become to be known as Graham’s law.