Crystallization is the process by which a solid forms, where the atoms or molecules are organized into a structure known as a crystal. Some of the ways by which crystals form are precipitating from a solution, freezing, or more deposition directly from a gas. Attributes of the resulting crystal depend on factors such as temperature, air pressure, in the case of liquid crystals, time of fluid evaporation. Crystallization occurs in two major steps; the first is nucleation, the appearance of a crystalline phase from either a supercooled liquid or a supersaturated solvent. The second step is known as crystal growth, the increase in the size of particles and leads to a crystal state. An important feature of this step is that loose particles form layers at the crystal's surface lodge themselves into open inconsistencies such as pores, etc; the majority of minerals and organic molecules crystallize and the resulting crystals are of good quality, i.e. without visible defects. However, larger biochemical particles, like proteins, are difficult to crystallize.
The ease with which molecules will crystallize depends on the intensity of either atomic forces, intermolecular forces or intramolecular forces. Crystallization is a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs. In chemical engineering, crystallization occurs in a crystallizer. Crystallization is therefore related to precipitation, although the result is not amorphous or disordered, but a crystal; the crystallization process consists of two major events and crystal growth which are driven by thermodynamic properties as well as chemical properties. In crystallization Nucleation is the step where the solute molecules or atoms dispersed in the solvent start to gather into clusters, on the microscopic scale, that become stable under the current operating conditions; these stable clusters constitute the nuclei. Therefore, the clusters need to reach a critical size; such critical size is dictated by many different factors.
It is at the stage of nucleation that the atoms or molecules arrange in a defined and periodic manner that defines the crystal structure — note that "crystal structure" is a special term that refers to the relative arrangement of the atoms or molecules, not the macroscopic properties of the crystal, although those are a result of the internal crystal structure. The crystal growth is the subsequent size increase of the nuclei that succeed in achieving the critical cluster size. Crystal growth is a dynamic process occurring in equilibrium where solute molecules or atoms precipitate out of solution, dissolve back into solution. Supersaturation is one of the driving forces of crystallization, as the solubility of a species is an equilibrium process quantified by Ksp. Depending upon the conditions, either nucleation or growth may be predominant over the other, dictating crystal size. Many compounds have the ability to crystallize with some having different crystal structures, a phenomenon called polymorphism.
Each polymorph is in fact a different thermodynamic solid state and crystal polymorphs of the same compound exhibit different physical properties, such as dissolution rate, melting point, etc. For this reason, polymorphism is of major importance in industrial manufacture of crystalline products. Additionally, crystal phases can sometimes be interconverted by varying factors such as temperature. There are many examples of natural process. Geological time scale process examples include: Natural crystal formation. Human time scale process examples include: Snow flakes formation. Crystal formation can be divided into two types, where the first type of crystals are composed of a cation and anion known as a salt, such as sodium acetate; the second type of crystals are composed for example menthol. Crystal formation can be achieved by various methods, such as: cooling, addition of a second solvent to reduce the solubility of the solute, solvent layering, changing the cation or anion, as well as other methods.
The formation of a supersaturated solution does not guarantee crystal formation, a seed crystal or scratching the glass is required to form nucleation sites. A typical laboratory technique for crystal formation is to dissolve the solid in a solution in which it is soluble at high temperatures to obtain supersaturation; the hot mixture is filtered to remove any insoluble impurities. The filtrate is allowed to cool. Crystals that form are filtered and washed with a solvent in which they are not soluble, but is miscible with the mother liquor; the process is repeated to increase the purity in a technique known as recrystallization. For biological molecules in which the solvent channels continue to be present to retain the three dimensional structure intact, microbatch crystallization under oil and vapor diffusion methods have been the common methods. Equipment for the main industrial processes for crystallization. Tank crystallizers. Tank crystallization is an old method still used in some specialized cases.
Saturated solutions, in tank crystallization, are allowed to cool in open tanks. After a period of time the mother liquo
Sofia is the capital and largest city of Bulgaria. The city is at the foot of Vitosha Mountain in the western part of the country. Being in the centre of the Balkan peninsula, it is midway between the Black Sea and the Adriatic Sea, closest to the Aegean Sea. Sofia has been an area of human habitation since at least 7000 BC; the recorded history of Sofia begins with the attestation of the conquest of Serdica by the Roman Republic in 29 BC from the Celtic tribe Serdi, raided by Huns in 343-347 AD and 447 AD, conquered by Visigoths in 376-382 AD, conquered by Avars and Slavs in 617 AD, on 9th April, 809 Serdica was surrendered to Krum of Bulgaria. In 1018, the Byzantines ended Bulgarian rule; the town was conquered by the Pechenegs in 1048 and 1078, by the Magyars and Serbs in 1183, by the Crusaders in 1095 and 1190. The rule of the Second Bulgarian Empire lasted from 1194 until its conquest by the Ottomans in 1382.. From 1520 to 1836, Sofia was the regional capital of Rumelia Eyalet, the Ottoman Empire's key province in Europe.
Bulgarian rule was restored in 1878. During World War II Sofia was bombarded by the UK and US Air Forces and at the end of the war, it was seized by the Soviet Army. Being Bulgaria's primate city, Sofia is a hometown of many of the major local universities, cultural institutions and commercial companies. Sofia is one of the top 10 best places for start-up businesses in the world in information technologies, according to Bulgarian National Television. Sofia was Europe's most affordable capital to visit in 2013; the population of Sofia declined down from 70,000 in the late 18th century, through 19,000 in 1870, to 11,649 in 1878 and began increasing. Sofia hosts some 1.23 million residents within a territory of 492 km2, a concentration of 17.5% of the country population within the 200th percentile of the country territory. The urban area of Sofia hosts some 1.54 million residents within 5723 km², which comprises Sofia City Province and parts of Sofia Province and Pernik Province, representing 5.16% of the country territory.
The metropolitan area of Sofia is based upon one hour of car travel time, stretches internationally and includes Dimitrovgrad in Serbia. Unlike most European metropolitan areas, it is not to be defined as a functional metropolitan area, but is of the type with "limited variety of functions"; the metropolitan region of Sofia is inhabited by a population of 1.68 million and is made up of the whole provinces Sofia City and Pernik, comprising more than 10,000 km². For the longest time the city possessed a Thracian name, derived from the tribe Serdi, who were either of Thracian, Celtic, or mixed Thracian-Celtic origin; the emperor Marcus Ulpius Traianus gave the city the combinative name of Ulpia Serdica. It seems that the first written mention of Serdica was made during his reign and the last mention was in the 19th century in a Bulgarian text. Other names given to Sofia, such as Serdonpolis and Triaditza, were mentioned by Byzantine Greek sources or coins; the Slavic name Sredets, related to "middle" and to the city's earliest name, first appeared on paper in an 11th-century text.
The city was called Atralisa by the Arab traveller Idrisi and Strelisa, Stralitsa or Stralitsion by the Crusaders. The name Sofia comes from the Saint Sofia Church, as opposed to the prevailing Slavic origin of Bulgarian cities and towns; the origin is in the Greek word sophia "wisdom", which may derive from the Egyptian word sbÅ "teach, learn or wise" provided b oftentimes turns into ph in Egyptian to Greek translations. The earliest works where this latest name is registered are the duplicate of the Gospel of Serdica, in a dialogue between two salesmen from Dubrovnik around 1359, in the 14th-century Vitosha Charter of Bulgarian tsar Ivan Shishman and in a Ragusan merchant's notes of 1376. In these documents the city is called Sofia, but at the same time the region and the city's inhabitants are still called Sredecheski, which continued until the 20th century; the city became somehow popular to the Ottomans by the name Sofya. In 1879 there was a dispute about what the name of the new Bulgarian capital should be, when the citizens created a committee of famous people, insisting for the Slavic name.
A compromise arose, officialisation of Sofia for the nationwide institutions, while legitimating the title Sredets for the administrative and church institutions, before the latter was abandoned through the years. The city's name is pronounced by Bulgarians with a stress on the'o', in contrast with the tendency of foreigners to place the stress on'i'; the female given name "Sofia" is pronounced by Bulgarians with a stress on the'i'. Sofia City Province has an area of 1344 km2. Sofia's development as a significant settlement owes much to its central position in the Balkans, it is situated in western Bulgaria, at the northern foot of the Vitosha mountain, in the Sofia Valley, surrounded by the Balkan mountains to the north. The valley has an average altitude of 550 metres. Unlike most European capitals, Sofia does not have any large rivers or bridges, but is surrounded by comparatively high mountains on all sides. Three mountain passes lead to the city, which have been key roads since antiquity, Vitosha being the watershed between Black and Aegean Seas.
A number of l
Berkovitsa is a town and ski resort in northwestern Bulgaria. It is the administrative centre of the homonymous Berkovitsa Municipality, Montana Province and is close to the town of Varshets; as of December 2009, it has a population of 13,917 inhabitants. Berkovitsa is situated on the northern slope of Kom Peak of the Berkovska Stara Planina Mountain along the valley of the Berkovitsa River, a tributary to the Barziya River, at an altitude above sea level 405 m; the town was mentioned for the first time in Ottoman documents of 1488. It is near the site of an old fortified settlement on the road from Sofia to Lom; the remains of the fortress and a church were discovered on high ground at Kaleto, just to the west of the present-day town. The former settlement was known as early as the reign of King Kaloyan and was mentioned as a border settlement in the period of the Vidin Kingdom. Berkovitsa Glacier, on Livingston Island in the South Shetland Islands, Antarctica, is named for Berkovitsa. Berkovitsa has a terminus railway station.
It has access to the railway connecting Vidin and Vratsa. There are four trains per day. Berkovitsa is twinned with: Dzerzhinsk, Russia Zaječar, Serbia Dimitrovgrad, Serbia Timo Angelov, member of IMARO Official website Nikola Gruev’s photo gallery of Berkovitsa Berkovitsa at Domino.bg
Bulgarian Academy of Sciences
The Bulgarian Academy of Sciences is the National Academy of Bulgaria, established in 1869. The Academy, located in Sofia, is autonomous and has a Society of Academicians, Correspondent Members and Foreign Members, it publishes and circulates different scientific works, encyclopedias and journals, runs its own publishing house. Stefan Vodenicharov has been president of the BAS since 2012, its budget in 2009 was 42.7 million euro. The Bulgarian Space Agency, part of the BAS, has a budget of 1 million euro; as Bulgaria was part of the Ottoman Empire, Bulgarian émigrés founded the Bulgarian Literary Society on 26 September 1869, in Brăila in the Kingdom of Romania. The first Statutes accepted were: Board of Trustees Nikolai Tsenov – President Vasilaki Mihailidi Petraki Simov Kostaki Popovich Stefan BeronActing members: Marin Drinov – Chairman Vasil Drumev – Member Vasil D. Stoyanov – SecretaryThe following year, the Literary Society began issuing the Periodical Journal, its official publication, in 1871 elected its first honorary member - Gavril Krastevich.
In 1878, shortly after Bulgaria's liberation from Ottoman rule, the General Assembly voted to move the seat of the Society from Brăila to Sofia, on 1 March 1893 the BLS moved into its own building, right next to where the Bulgarian Parliament is seated. The BLS headquarters were completed in 1892; the building was expanded during the 1920s. The Bulgarian Literary Society adopted its present-day name in 1911, Ivan Geshov became the Academy's first president; the BAS became a member of the Union of Slavonic Academies and Scientific Communities in 1913, was accepted as member of the International Council of Scientific Unions in 1931. The BAS has 9 main sections, more broadly united under three main branches: Natural and engineering sciences, Biological and agrarian sciences and Social sciences and art; each consists of independent scientific institutes and other sections. Institute of Mathematics and Informatics Institute of Mechanics Institute of Information and Communication Technologies National Laboratory of Computer Virology Institute for Nuclear Research and Nuclear Energy Institute of Solid State Physics Institute of Electronics Institute of Astronomy National Astronomical Observatory - Rozhen Astronomical Observatory Belogradchik Central Laboratory of Solar Energy and New Energy Sources Central Laboratory for Applied Physics - Plovdiv Central Laboratory of Optical Storage and Processing of Information Institute of General and Inorganic Chemistry Institute of Organic Chemistry with a Center of Phyto-Chemistry Institute of Physical Chemistry Institute of Catalysis Institute of Electrochemistry and Energy Systems Institute of Chemical Engineering Central Laboratory of Photoprocesses Institute of Polymers Institute of Neurobiology Institute of Molecular Biology Institute of Genetics Institute of Physiology Institute of Plant Physiology Institute of Microbiology Institute of Experimental Morphology and Anthropology Institute of Botany Institute of Zoology Forest Research Institute Institute of Experimental Pathology and Parasitology Institute of Biology and Immunology of Reproduction Institute of Biophysics and Biomedical Engineering National Museum of Natural History Central Laboratory of General Ecology Geological Institute Geophysical Institute National Institute of Meteorology and Hydrology Central Laboratory for Geodesy Central Laboratory of Mineralogy and Crystallography Institute of Oceanology Geographical Institute Space Research Institute Central Laboratory of Solar - Terrestrial Influences Central Laboratory for Seismic Mechanics and Earthquake Engineering Institute of Water Problems Institute of Metal Science Central Laboratory of Physico-Chemical Mechanics Institute of Computer and Communication Systems Institute of Information Technologies Institute of Control and System Research Central Laboratory of Mechatronics and Instrumentation Bulgarian Ship Hydrodynamics Centre Institute of Bulgarian Language Institute of Literature Institute for Balkan Studies and Center for Thracology Institute for History Studies Institute for Ethnology and Folklore Studies with Ethnographic Museum, comprising the former Institute for Folklore Studies Ethnographic Institute with Museum Institute for Arts Studies, comprising the former Center for Architectural Studies Institute of Art Studies National Archaeological Institute and Museum Scientific Center for Cyrillo-Methodian Studies Institute for Economic Studies Institute for the State and Law Institute for Population and Human Studies, comprising the former Institute of Psychology Center for Population Studies Institute for the Study of Societies and Knowledge, comprising the former Institute of Sociology Institute of Philosophical Studies Center for Science Studies and History of Science Central Administration of BAS Central Library of BAS Scientific Archives of BAS Academic Publishing House "Prof. Marin Drinov" Botanical Garden National Centre on Nanosciences and Nanotechnology Bulgarian Encyclopedia Scientific Information Center Social - Utility Service Center for National Security Research Research Development and Implementation Association "Scientific Instrumentation" Laboratory of Telematics Ph.
D. Research Career Development Center Academia Peak and Camp Academia on Livingston Island in the South Shetland Islands, Antarctica are named for the Bulgarian Academy of Sciences in appreciation of Academy’s contribution to the Antarctic exploration. Camp Academia Bulgarian Academy of Sciences official website
Système universitaire de documentation
The système universitaire de documentation or SUDOC is a system used by the libraries of French universities and higher education establishments to identify and manage the documents in their possession. The catalog, which contains more than 10 million references, allows students and researcher to search for bibliographical and location information in over 3,400 documentation centers, it is maintained by the Bibliographic Agency for Higher Education. Official website
Virtual International Authority File
The Virtual International Authority File is an international authority file. It is a joint project of several national libraries and operated by the Online Computer Library Center. Discussion about having a common international authority started in the late 1990s. After a series of failed attempts to come up with a unique common authority file, the new idea was to link existing national authorities; this would present all the benefits of a common file without requiring a large investment of time and expense in the process. The project was initiated by the US Library of Congress, the German National Library and the OCLC on August 6, 2003; the Bibliothèque nationale de France joined the project on October 5, 2007. The project transitioned to being a service of the OCLC on April 4, 2012; the aim is to link the national authority files to a single virtual authority file. In this file, identical records from the different data sets are linked together. A VIAF record receives a standard data number, contains the primary "see" and "see also" records from the original records, refers to the original authority records.
The data are available for research and data exchange and sharing. Reciprocal updating uses the Open Archives Initiative Protocol for Metadata Harvesting protocol; the file numbers are being added to Wikipedia biographical articles and are incorporated into Wikidata. VIAF's clustering algorithm is run every month; as more data are added from participating libraries, clusters of authority records may coalesce or split, leading to some fluctuation in the VIAF identifier of certain authority records. Authority control Faceted Application of Subject Terminology Integrated Authority File International Standard Authority Data Number International Standard Name Identifier Wikipedia's authority control template for articles Official website VIAF at OCLC
A chemist is a scientist trained in the study of chemistry. Chemists study the composition of its properties. Chemists describe the properties they study in terms of quantities, with detail on the level of molecules and their component atoms. Chemists measure substance proportions, reaction rates, other chemical properties; the word'chemist' is used to address Pharmacists in Commonwealth English. Chemists use this knowledge to learn the composition and properties of unfamiliar substances, as well as to reproduce and synthesize large quantities of useful occurring substances and create new artificial substances and useful processes. Chemists may specialize in any number of subdisciplines of chemistry. Materials scientists and metallurgists share skills with chemists; the work of chemists is related to the work of chemical engineers, who are concerned with the proper design and evaluation of the most cost-effective large-scale chemical plants and work with industrial chemists on the development of new processes and methods for the commercial-scale manufacture of chemicals and related products.
The roots of chemistry can be traced to the phenomenon of burning. Fire was a mystical force that transformed one substance into another and thus was of primary interest to mankind, it was fire. After gold was discovered and became a precious metal, many people were interested to find a method that could convert other substances into gold; this led to the protoscience called alchemy. The word chemist is derived from an abbreviation of alchimista. Alchemists discovered many chemical processes. Chemistry as we know it today, was invented by Antoine Lavoisier with his law of conservation of mass in 1783; the discoveries of the chemical elements has a long history culminating in the creation of the periodic table by Dmitri Mendeleev. The Nobel Prize in Chemistry created in 1901 gives an excellent overview of chemical discovery since the start of the 20th century. Jobs for chemists require at least a bachelor's degree, but many positions those in research, require a Master of Science or a Doctor of Philosophy.
Most undergraduate programs emphasize mathematics and physics as well as chemistry because chemistry is known as "the central science", thus chemists ought to have a well-rounded knowledge about science. At the Master's level and higher, students tend to specialize in a particular field. Fields of specialization include biochemistry, nuclear chemistry, organic chemistry, inorganic chemistry, polymer chemistry, analytical chemistry, physical chemistry, theoretical chemistry, quantum chemistry, environmental chemistry, thermochemistry. Postdoctoral experience may be required for certain positions. Workers whose work involves chemistry, but not at a complexity requiring an education with a chemistry degree, are referred to as chemical technicians; such technicians do such work as simpler, routine analyses for quality control or in clinical laboratories, having an associate degree. A chemical technologist has more education or experience than a chemical technician but less than a chemist having a bachelor's degree in a different field of science with an associate degree in chemistry or having the same education as a chemical technician but more experience.
There are degrees specific to become a chemical technologist, which are somewhat distinct from those required when a student is interested in becoming a professional chemist. A Chemical technologist is more involved in the management and operation of the equipment and instrumentation necessary to perform chemical analyzes than a chemical technician, they are part of the team of a chemical laboratory in which the quality of the raw material, intermediate products and finished products is analyzed. They perform functions in the areas of environmental quality control and the operational phase of a chemical plant. In addition to all the training given to chemical technologists in their respective degree, a chemist is trained to understand more details related to chemical phenomena so that the chemist can be capable of more planning on the steps to achieve a distinct goal via a chemistry-related endeavor; the higher the competency level achieved in the field of chemistry, the higher the responsibility given to that chemist and the more complicated the task might be.
Chemistry, as a field, have so many applications that different tasks and objectives can be given to workers or scientists with these different levels of education or experience. The specific title of each job varies from position to position, depending on factors such as the kind of industry, the routine level of the task, the current needs of a particular enterprise, the size of the enterprise or hiring firm, the philosophy and management principles of the hiring firm, the visibility of the competency and individual achievements of the one seeking employment, economic factors such as recession or economic depression, among other factors, so this makes it difficult to categorize the exact roles of these chemistry-related workers as standard for that given level of education; because of these factors affecting exact job titles with distinct responsibilities, some chemists might begin doing technician tasks while other chemists might begin doing more complicated tasks than those of a technician, such as tasks th