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Active Directory

Active Directory (AD) is a directory service developed by Microsoft for Windows domain networks. Windows Server operating systems include it as a set of processes and services. Originally, only centralized domain management used Active Directory. However, it ultimately became an umbrella title for various directory-based identity-related services.

A domain controller is a server running the Active Directory Domain Service (AD DS) role. It authenticates and authorizes all users and computers in a Windows domain-type network, assigning and enforcing security policies for all computers and installing or updating software. For example, when a user logs into a computer which is part of a Windows domain, Active Directory checks the submitted username and password and determines whether the user is a system administrator or a non-admin user. Furthermore, it allows the management and storage of information, provides authentication and authorization mechanisms, and establishes a framework to deploy other related services: Certificate Services, Active Directory Federation Services, Lightweight Directory Services, and Rights Management Services.

Active Directory uses Lightweight Directory Access Protocol (LDAP) versions 2 and 3, Microsoft's version of Kerberos, and DNS.

Robert R. King defined it in the following way:

"'A domain represents a database. That database holds records about network services-things like computers, users, groups and other things that use, support, or exist on a network. The domain database is, in effect, Active Directory.'"

History
Like many information-technology efforts, Active Directory originated out of a democratization of design using Requests for Comments (RFCs). The Internet Engineering Task Force (IETF) oversees the RFC process and has accepted numerous RFCs initiated by widespread participants. For example, LDAP underpins Active Directory. Also, X.500 directories and the Organizational Unit preceded the Active Directory concept that uses those methods. The LDAP concept began to emerge even before the founding of Microsoft in April 1975, with RFCs as early as 1971. RFCs contributing to LDAP include RFC 1823 (on the LDAP API, August 1995), RFC 2307, RFC 3062 , and RFC 4533.

Microsoft previewed Active Directory in 1999, released it first with Windows 2000 Server edition, and revised it to extend functionality and improve administration in Windows Server 2003. Active Directory support was also added to Windows 95, Windows 98, and Windows NT 4.0 via patch, with some unsupported features. Additional improvements came with subsequent versions of Windows Server. In Windows Server 2008, Microsoft added further services to Active Directory, such as Active Directory Federation Services. The part of the directory in charge of managing domains, which was a core part of the operating system, was renamed Active Directory Domain Services (ADDS) and became a server role like others. "Active Directory" became the umbrella title of a broader range of directory-based services. According to Byron Hynes, everything related to identity was brought under Active Directory's banner.

Active Directory Services
Active Directory Services consist of multiple directory services. The best known is Active Directory Domain Services, commonly abbreviated as AD DS or simply AD.

Domain Services
Active Directory Domain Services (AD DS) is the foundation of every Windows domain network. It stores information about domain members, including devices and users, verifies their credentials, and defines their access rights. The server running this service is called a domain controller. A domain controller is contacted when a user logs into a device, accesses another device across the network, or runs a line-of-business Metro-style app sideloaded into a machine.

Other Active Directory services (excluding LDS, as described below) and most Microsoft server technologies rely on or use Domain Services; examples include Group Policy, Encrypting File System, BitLocker, Domain Name Services, Remote Desktop Services, Exchange Server, and SharePoint Server.

The self-managed Active Directory DS must be distinct from managed Azure AD DS, a cloud product.

Lightweight Directory Services
Active Directory Lightweight Directory Services (AD LDS), previously called Active Directory Application Mode (ADAM), implements the LDAP protocol for AD DS. It runs as a service on Windows Server and offers the same functionality as AD DS, including an equal API. However, AD LDS does not require the creation of domains or domain controllers. It provides a Data Store for storing directory data and a Directory Service with an LDAP Directory Service Interface. Unlike AD DS, multiple AD LDS instances can operate on the same server.

Certificate Services
Active Directory Certificate Services (AD CS) establishes an on-premises public key infrastructure. It can create, validate, revoke and perform other similar actions, public key certificates for internal uses of an organization. These certificates can be used to encrypt files (when used with Encrypting File System), emails (per S/MIME standard), and network traffic (when used by virtual private networks, Transport Layer Security protocol or IPSec protocol).

AD CS predates Windows Server 2008, but its name was simply Certificate Services.

AD CS requires an AD DS infrastructure.

Federation Services
Active Directory Federation Services (AD FS) is a single sign-on service. With an AD FS infrastructure in place, users may use several web-based services (e.g. internet forum, blog, online shopping, webmail) or network resources using only one set of credentials stored at a central location, as opposed to having to be granted a dedicated set of credentials for each service. AD FS uses many popular open standards to pass token credentials such as SAML, OAuth or OpenID Connect. AD FS supports encryption and signing of SAML assertions. AD FS's purpose is an extension of that of AD DS: The latter enables users to authenticate with and use the devices that are part of the same network, using one set of credentials. The former enables them to use the same set of credentials in a different network.

As the name suggests, AD FS works based on the concept of federated identity.

AD FS requires an AD DS infrastructure, although its federation partner may not.

Rights Management Services
Active Directory Rights Management Services (AD RMS), previously known as Rights Management Services or RMS before Windows Server 2008, is server software that allows for information rights management, included with Windows Server. It uses encryption and selective denial to restrict access to various documents, such as corporate e-mails, Microsoft Word documents, and web pages. It also limits the operations authorized users can perform on them, such as viewing, editing, copying, saving, or printing. IT administrators can create pre-set templates for end users for convenience, but end users can still define who can access the content and what actions they can take.

Logical structure
Active Directory is a service comprising a database and executable code. It is responsible for managing requests and maintaining the database. The Directory System Agent is the executable part, a set of Windows services and processes that run on Windows 2000 and later. Accessing the objects in Active Directory databases is possible through various interfaces such as LDAP, ADSI, messaging API, and Security Accounts Manager services.

Objects used
Active Directory structures consist of information about objects classified into two categories: resources (such as printers) and security principals (which include user or computer accounts and groups). Each security principal is assigned a unique security identifier (SID). An object represents a single entity, such as a user, computer, printer, or group, along with its attributes. Some objects may even contain other objects within them. Each object has a unique name, and its definition is a set of characteristics and information by a schema, which determines the storage in the Active Directory.

Administrators can extend or modify the schema using the schema object when needed. However, because each schema object is integral to the definition of Active Directory objects, deactivating or changing them can fundamentally alter or disrupt a deployment. Modifying the schema affects the entire system automatically, and new objects cannot be deleted, only deactivated. Changing the schema usually requires planning.

Forests, trees, and domains
In an Active Directory network, the framework that holds objects has different levels: the forest, tree, and domain. Domains within a deployment contain objects stored in a single replicable database, and the DNS name structure identifies their domains, the namespace. A domain is a logical group of network objects such as computers, users, and devices that share the same Active Directory database.

On the other hand, a tree is a collection of domains and domain trees in a contiguous namespace linked in a transitive trust hierarchy. The forest is at the top of the structure, a collection of trees with a standard global catalog, directory schema, logical structure, and directory configuration. The forest is a secure boundary that limits access to users, computers, groups, and other objects.

Organizational units
The objects held within a domain can be grouped into organizational units (OUs). OUs can provide hierarchy to a domain, ease its administration, and can resemble the organization's structure in managerial or geographical terms. OUs can contain other OUs—domains are containers in this sense. Microsoft recommends using OUs rather than domains for structure and simplifying the implementation of policies and administration. The OU is the recommended level at which to apply group policies, which are Active Directory objects formally named group policy objects (GPOs), although policies can also be applied to domains or sites (see below). The OU is the level at which administrative powers are commonly delegated, but delegation can be performed on individual objects or attributes as well.

Organizational units do not each have a separate namespace. As a consequence, for compatibility with Legacy NetBios implementations, user accounts with an identical sAMAccountName are not allowed within the same domain even if the accounts objects are in separate OUs. This is because sAMAccountName, a user object attribute, must be unique within the domain. However, two users in different OUs can have the same common name (CN), the name under which they are stored in the directory itself such as "fred.staff-ou.domain" and "fred.student-ou.domain", where "staff-ou" and "student-ou" are the OUs.

In general, the reason for this lack of allowance for duplicate names through hierarchical directory placement is that Microsoft primarily relies on the principles of NetBIOS, which is a flat-namespace method of network object management that, for Microsoft software, goes all the way back to Windows NT 3.1 and MS-DOS LAN Manager. Allowing for duplication of object names in the directory, or completely removing the use of NetBIOS names, would prevent backward compatibility with legacy software and equipment. However, disallowing duplicate object names in this way is a violation of the LDAP RFCs on which Active Directory is supposedly based.

As the number of users in a domain increases, conventions such as "first initial, middle initial, last name" (Western order) or the reverse (Eastern order) fail for common family names like Li (李), Smith or Garcia. Workarounds include adding a digit to the end of the username. Alternatives include creating a separate ID system of unique employee/student ID numbers to use as account names in place of actual users' names and allowing users to nominate their preferred word sequence within an acceptable use policy.

Because duplicate usernames cannot exist within a domain, account name generation poses a significant challenge for large organizations that cannot be easily subdivided into separate domains, such as students in a public school system or university who must be able to use any computer across the network.

Shadow groups
In Microsoft's Active Directory, OUs do not confer access permissions, and objects placed within OUs are not automatically assigned access privileges based on their containing OU. It represents a design limitation specific to Active Directory, and other competing directories, such as Novell NDS, can set access privileges through object placement within an OU.

Active Directory requires a separate step for an administrator to assign an object in an OU as a group member also within that OU. Using only the OU location to determine access permissions is unreliable since the entity might not have been assigned to the group object for that OU yet.

A common workaround for an Active Directory administrator is to write a custom PowerShell or Visual Basic script to automatically create and maintain a user group for each OU in their Directory. The scripts run periodically to update the group to match the OU's account membership. However, they cannot instantly update the security groups anytime the directory changes, as occurs in competing directories, as security is directly implemented into the Directory. Such groups are known as shadow groups. Once created, these shadow groups are selectable in place of the OU in the administrative tools. Microsoft's Server 2008 reference documentation mentions shadow groups but does not provide instructions on creating them. Additionally, there are no available server methods or console snap-ins for managing these groups.

An organization must determine the structure of its information infrastructure by dividing it into one or more domains and top-level OUs. This decision is critical and can base on various models such as business units, geographical locations, IT service, object type, or a combination of these models. The immediate purpose of organizing OUs is to simplify administrative delegation and, secondarily, to apply group policies. While OUs serve as an administrative boundary, the forest itself is the only security boundary. All other domains must trust any administrator in the forest to maintain security.

Partitions
The Active Directory database is organized in partitions, each holding specific object types and following a particular replication pattern. Microsoft often refers to these partitions as 'naming contexts. The 'Schema' partition defines object classes and attributes within the forest. The 'Configuration' partition contains information on the physical structure and configuration of the forest (such as the site topology). Both replicate all domains in the forest. The 'Domain' partition holds all objects created in that domain and replicates only within it.

Physical structure
Sites are physical (rather than logical) groupings defined by one or more IP subnets. AD also defines connections, distinguishing low-speed (e.g., WAN, VPN) from high-speed (e.g., LAN) links. Site definitions are independent of the domain and OU structure and are shared across the forest. Sites play a crucial role in managing network traffic created by replication and directing clients to their nearest domain controllers (DCs). Microsoft Exchange Server 2007 uses the site topology for mail routing. Administrators can also define policies at the site level.

The Active Directory information is physically held on one or more peer domain controllers, replacing the NT PDC/BDC model. Each DC has a copy of the Active Directory. Member servers joined to Active Directory that are not domain controllers are called Member Servers. In the domain partition, a group of objects acts as copies of domain controllers set up as global catalogs. These global catalog servers offer a comprehensive list of all objects located in the forest.

Global Catalog servers replicate all objects from all domains to themselves, providing an international listing of entities in the forest. However, to minimize replication traffic and keep the GC's database small, only selected attributes of each object are replicated, called the partial attribute set (PAS). The PAS can be modified by modifying the schema and marking features for replication to the GC. Earlier versions of Windows used NetBIOS to communicate. Active Directory is fully integrated with DNS and requires TCP/IP—DNS. To fully operate, the DNS server must support SRV resource records, also known as service records.

Replication
Active Directory uses multi-master replication to synchronize changes, meaning replicas pull changes from the server where the change occurred rather than being pushed to them. The Knowledge Consistency Checker (KCC) uses defined sites to manage traffic and create a replication topology of site links. Intra-site replication occurs frequently and automatically due to change notifications, which prompt peers to begin a pull replication cycle. Replication intervals between different sites are usually less consistent and don't usually use change notifications. However, it's possible to set it up to be the same as replication between locations on the same network if needed.

Each DS3, T1, and ISDN link can have a cost, and the KCC alters the site link topology accordingly. Replication may occur transitively through several site links on same-protocol site link bridges if the price is low. However, KCC automatically costs a direct site-to-site link lower than transitive connections. A bridgehead server in each zone can send updates to other DCs in the exact location to replicate changes between sites. To configure replication for Active Directory zones, activate DNS in the domain based on the site.

To replicate Active Directory, Remote Procedure Calls (RPC) over IP (RPC/IP) are used. SMTP is used to replicate between sites but only for modifications in the Schema, Configuration, or Partial Attribute Set (Global Catalog) GCs. It's not suitable for reproducing the default Domain partition.

Implementation
Generally, a network utilizing Active Directory has more than one licensed Windows server computer. Backup and restore of Active Directory are possible for a network with a single domain controller. However, Microsoft recommends more than one domain controller to provide automatic failover protection of the directory. Domain controllers are ideally single-purpose for directory operations only and should not run any other software or role.

Since certain Microsoft products, like SQL Server and Exchange, can interfere with the operation of a domain controller, isolation of these products on additional Windows servers is advised. Combining them can complicate the configuration and troubleshooting of the domain controller or the other installed software more complex. If planning to implement Active Directory, a business should purchase multiple Windows server licenses to have at least two separate domain controllers. Administrators should consider additional domain controllers for performance or redundancy and individual servers for tasks like file storage, Exchange, and SQL Server since this will guarantee that all server roles are adequately supported.

One way to lower the physical hardware costs is by using virtualization. However, for proper failover protection, Microsoft recommends not running multiple virtualized domain controllers on the same physical hardware.

Database
The Active-Directory database, the directory store, in Windows 2000 Server uses the JET Blue-based Extensible Storage Engine (ESE98). Each domain controller's database is limited to 16 terabytes and 2 billion objects (but only 1 billion security principals). Microsoft has created NTDS databases with more than 2 billion objects. NT4's Security Account Manager could support up to 40,000 objects. It has two main tables: the data table and the link table. Windows Server 2003 added a third main table for security descriptor single instancing.

Programs may access the features of Active Directory via the COM interfaces provided by Active Directory Service Interfaces.

Trusting
To allow users in one domain to access resources in another, Active Directory uses trusts.

Trusts inside a forest are automatically created when domains are created. The forest sets the default boundaries of trust, and implicit, transitive trust is automatic for all domains within a forest.

Terminology

 * One-way trust
 * One domain allows access to users on another domain, but the other domain does not allow access to users on the first domain.

 * Two-way trust
 * Two domains allow access to users on both domains.

 * Trusted domain
 * The domain that is trusted; whose users have access to the trusting domain.

 * Transitive trust
 * A trust that can extend beyond two domains to other trusted domains in the forest.

 * Intransitive trust
 * A one way trust that does not extend beyond two domains.

 * Explicit trust
 * A trust that an admin creates. It is not transitive and is one way only.

 * Cross-link trust
 * An explicit trust between domains in different trees or the same tree when a descendant/ancestor (child/parent) relationship does not exist between the two domains.

 * Shortcut
 * Joins two domains in different trees, transitive, one- or two-way.

 * Forest trust
 * Applies to the entire forest. Transitive, one- or two-way.

 * Realm
 * Can be transitive or nontransitive (intransitive), one- or two-way.

 * External
 * Connect to other forests or non-Active Directory domains. Nontransitive, one- or two-way.
 * PAM trust
 * A one-way trust used by Microsoft Identity Manager from a (possibly low-level) production forest to a (Windows Server 2016 functionality level) 'bastion' forest, which issues time-limited group memberships.

Management tools
Microsoft Active Directory management tools include:
 * Active Directory Administrative Center (Introduced with Windows Server 2012 and above),
 * Active Directory Users and Computers,
 * Active Directory Domains and Trusts,
 * Active Directory Sites and Services,
 * ADSI Edit,
 * Local Users and Groups,
 * Active Directory Schema snap-ins for Microsoft Management Console (MMC),
 * SysInternals ADExplorer.

These management tools may not provide enough functionality for efficient workflow in large environments. Some third-party tools extend the administration and management capabilities. They provide essential features for a more convenient administration process, such as automation, reports, integration with other services, etc.

Unix integration
Varying levels of interoperability with Active Directory can be achieved on most Unix-like operating systems (including Unix, Linux, Mac OS X or Java and Unix-based programs) through standards-compliant LDAP clients, but these systems usually do not interpret many attributes associated with Windows components, such as Group Policy and support for one-way trusts.

Third parties offer Active Directory integration for Unix-like platforms, including:
 * PowerBroker Identity Services, formerly Likewise (BeyondTrust, formerly Likewise Software) – Allows a non-Windows client to join Active Directory
 * ADmitMac (Thursby Software Systems)
 * Samba (free software under GPLv3) – Can act as a domain controller

The schema additions shipped with Windows Server 2003 R2 include attributes that map closely enough to RFC 2307 to be generally usable. The reference implementation of RFC 2307, nss_ldap and pam_ldap provided by PADL.com, support these attributes directly. The default schema for group membership complies with RFC 2307bis (proposed). Windows Server 2003 R2 includes a Microsoft Management Console snap-in that creates and edits the attributes.

An alternative option is to use another directory service as non-Windows clients authenticate to this while Windows Clients authenticate to Active Directory. Non-Windows clients include 389 Directory Server (formerly Fedora Directory Server, FDS), ViewDS v7.2 XML Enabled Directory, and Sun Microsystems Sun Java System Directory Server. The latter two are both able to perform two-way synchronization with Active Directory and thus provide a "deflected" integration.

Another option is to use OpenLDAP with its translucent overlay, which can extend entries in any remote LDAP server with additional attributes stored in a local database. Clients pointed at the local database see entries containing both the remote and local attributes, while the remote database remains completely untouched.

Administration (querying, modifying, and monitoring) of Active Directory can be achieved via many scripting languages, including PowerShell, VBScript, JScript/JavaScript, Perl, Python, and Ruby. Free and non-free Active Directory administration tools can help to simplify and possibly automate Active Directory management tasks.

Since October 2017 Amazon AWS offers integration with Microsoft Active Directory.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Active Directory


text:
Arian (disambiguation)

Arianism is a nontrinitarian Christological doctrine.

Arian may also refer to:

Pertaining to Arius

 * A follower of Arius, a Christian presbyter in the 3rd and 4th century
 * Arian controversy, several controversies which divided the early Christian church
 * Arian fragment, Arian palimpsest

Groups of people

 * Arians or Areians, ancient people living in Ariana (origin of the modern name Iran)
 * Aryan, a term associated with the Proto-Indo-Iranians
 * Aryan race, the racial concept
 * An inhabitant of Aria (today's Herat, Afghanistan), used by the ancient and medieval Greeks (as Ἄρ(ε)ιοι/Ar(e)ioi) and Romans (as Arii)

Given name

 * Arian Asllani (born 1983), American rapper known as Action Bronson
 * Arian Bimo (born 1959), Albanian footballer
 * Arian Çuliqi, Albanian television director and screenwriter
 * Arian Foster (born 1986), American football player
 * Arian Hametaj (born 1957), Albanian footballer
 * Arián Iznaga, Cuban Paralympian sprinter
 * Arian Kabashi (born 1996), Kosovan footballer
 * Arian Kabashi (born 1997), Swedish footballer
 * Arlan Lerio (born 1976), Filipino boxer
 * Arian Leviste (born 1970), American electronic music artist, producer, and DJ
 * Arian Moayed (born 1980), Iranian-born American actor and theater producer
 * Arian Moreno (born 2003), Venezuelan footballer
 * Arian Nik (born 1994), British actor

Surname
Arian is a surname that originated in Ancient Persia

 * Arman Arian (born 1981), Iranian author, novelist and researcher
 * Asher Arian (1938–2010), American political scientist
 * Asma Arian, German-Qatari human rights activist
 * Laila Al-Arian (born 1980s), American broadcast journalist
 * Sami Al-Arian (born 1958), Palestinian-American civil rights activist
 * Praskovia Arian (1864–1949) Russian and Soviet writer and feminist
 * Bruce Arians (born 1952), American football coach and former player
 * Jake Arians (born 1978), American football player

Other

 * Arian (band), a pop band in Iran
 * Arian (newspaper), an Iranian newspaper since 1914
 * Arian, an outsider's name for a member of the Polish Brethren
 * Arian, a person born under the constellation Aries (astrology)

title: Arian (disambiguation)


text:
Aldona of Lithuania

Aldona (baptized Ona or Anna; her pagan name, Aldona, is known only from the writings of Maciej Stryjkowski; c. 1309 – 26 May 1339) was Queen consort of Poland (1333–1339), and a princess of the Grand Duchy of Lithuania. She was the daughter of Gediminas, Grand Duke of Lithuania.

Biography
Aldona married Casimir III of Poland, when he was 15 or 16 years old. The bride was probably of about the same age. The marriage took place on 30 April or 16 October 1325 and was a purely political maneuver to strengthen the first Polish–Lithuanian coalition against the Teutonic Knights. Casimir was seeking allies in the dispute over Pomerania with the Order. Gediminas had just undertaken an unsuccessful attempt to Christianize Lithuania. This coalition was a prelude to the Union of Krewo in 1385, and the Union of Lublin in 1569, which resulted in the creation of a new state, the Polish–Lithuanian Commonwealth. The details of the agreement are not known; however, it is known that Gediminas released all Polish captives, some 25,000 people, who returned to Poland. The importance of the marriage was attested by the fact that Władysław abandoned his earlier plans to marry his son to Jutta of Bohemia. The alliance was put into effect when joint Polish–Lithuanian forces organized an attack against the Margraviate of Brandenburg in 1326. However, the coalition was not strong and collapsed c. 1330. Yet, there is no evidence of fighting between Poland and Lithuania while Aldona was alive. Aldona died suddenly at the end of May 1339, and was buried in Kraków.

Aldona was remembered for her piety and devotion to music. She was accompanied by court musicians wherever she went. It was even suggested by Jan Długosz that the cymbals which were played in procession before her represented a pagan Lithuanian tradition. Her husband Casimir is known for his romantic affairs: after Aldona's death he married three more times.

Issue
Aldona had two daughters:
 * Cunigunde of Poland (died in 1357); married on 1 January 1345 Louis VI the Roman, the son of Louis IV, Holy Roman Emperor.
 * Elisabeth (1326–1361); married Bogislaus V, Duke of Pomerania. Elisabeth's daughter, Elizabeth of Pomerania, was the fourth wife of Charles IV, Holy Roman Emperor.

Film
Queen Aldona Anna is one of the main characters in the first season of Polish historical TV drama series "Korona Królów" ("The Crown of the Kings"). She is played by Marta Bryła.

title: Aldona of Lithuania


text:
Talk:Aldona of Lithuania

Old talk

 * Kunigunda became associated with Louis VI the Roman, duke of Bavaria, the son of Louis the Bavarian of the Holy Roman Empire.

Above removed from article - unclear what "associated with" means. Marriage? Illegitimate child?

 * Casimir III of Poland suggests that Cunigunde was indeed married. Martin

mr Bloomfield's polonisations are mistake
if Lithuanian start will change polish names - for example - KAZYMIERZ replace by lithuanisation - Kazimieras - this will be scandal and mistake But Mr Bloomfield have done polonisation of Lithuanian historycal names: Grand duke Gediminas changed into GIEDYMYN...WHY - it's nonsence in English...

Turbo Kestutis —Preceding unsigned comment added by 194.240.150.6   (talk • contribs) 19:45, 31 January 2006

title: Talk:Aldona of Lithuania


text:
Aron Nimzowitsch

Aron Nimzowitsch (Ārons Nimcovičs; Аро́н Иса́евич Нимцо́вич, Aron Isayevich Nimtsovich; 7 November 1886 – 16 March 1935) was a Latvian-born Danish chess player and writer. In the late 1920s, Nimzowitsch was one of the best chess players in the world. He was the foremost figure amongst the hypermoderns and wrote a very influential book on chess theory: My System (1925–1927). Nimzowitsch's seminal work Chess Praxis, originally published in German in 1929, was purchased by a pre-teen and future World Champion Tigran Petrosian and was to have a great influence on his development as a chess player.

Life
Born in Riga, then part of the Russian Empire, the Jewish Yiddish-speaking Nimzowitsch came from a wealthy family, where he learned chess from his father Shaya Abramovich Nimzowitsch (1860, Pinsk – 1918), who was a timber merchant. By 1897, the family lived in Dvinsk. Mother's name: Esphir Nohumovna Nimzowitsch (born Rabinovich, 1865, Polotsk – 1937), sister – Tsilya-Kreyna Pevzner, brothers Yakov, Osey and Benno. In 1904, he travelled to Berlin to study philosophy, but set aside his studies soon and began a career as a professional chess player that same year. He won his first international tournament at Munich 1906. Then, he tied for first with Alexander Alekhine at Saint Petersburg 1913/14 (the eighth All-Russian Masters' Tournament).

During the 1917 Russian Revolution, Nimzowitsch was in the Baltic war zone. He escaped being drafted into one of the armies by feigning madness, insisting that a fly was on his head. He then escaped to Berlin, and gave his first name as Arnold, possibly to avoid anti-Semitic persecution.

Nimzowitsch eventually moved to Copenhagen in 1922, where he lived for the rest of his life in one small rented room. In Copenhagen, he won the Nordic Championship twice, in 1924 and in 1934. He obtained Danish citizenship and lived in Denmark until his death in 1935.

Chess career
The height of Nimzowitsch's career was the late 1920s and early 1930s. Chessmetrics places him as the third best player in the world from 1927 to 1931, behind Alexander Alekhine and José Capablanca. His most notable successes were first-place finishes at Copenhagen 1923, Marienbad 1925, Dresden 1926, Hanover 1926, the Carlsbad 1929 chess tournament, and second place behind Alekhine at the San Remo 1930 chess tournament. Nimzowitsch never developed a knack for match play, though; his best match success was a draw with Alekhine, but the match consisted of only two games and took place in 1914, thirteen years before Alekhine became world champion.

Nimzowitsch never beat Capablanca (+0−5=6), but fared better against Alekhine (+3−9=9). He even beat Alekhine with the black pieces, in their short 1914 match at St. Petersburg. One of Nimzowitsch's most famous games is his celebrated immortal zugzwang game against Sämisch at Copenhagen 1923. Another game on this theme is his win over Paul Johner at Dresden 1926. When in form, Nimzowitsch was very dangerous with the black pieces, scoring many fine wins over top players.

Legacy
Nimzowitsch is considered one of the most important players and writers in chess history. His works influenced numerous other players, including Savielly Tartakower, Milan Vidmar, Richard Réti, Akiba Rubinstein, Mikhail Botvinnik, Bent Larsen, Viktor Korchnoi and Tigran Petrosian, and his influence is still felt today.

He wrote three books on chess strategy: Mein System (My System), 1925; Die Praxis meines Systems (The Practice of My System), 1929, commonly known as Chess Praxis; and Die Blockade (The Blockade), 1925, although much in this book is generally held to be a rehash of material already presented in Mein System. Mein System is considered to be one of the most influential chess books of all time. It sets out Nimzowitsch's most important ideas, while his second most influential work, Chess Praxis, elaborates upon these ideas, adds a few new ones, and has immense value as a stimulating collection of Nimzowitsch's own games accompanied by his idiosyncratic, hyperbolic commentary which is often as entertaining as instructive.

Nimzowitsch's chess theories, when first propounded, flew in the face of widely held orthodoxies enunciated by the dominant theorist of the era, Siegbert Tarrasch, and his disciples. Tarrasch's rigid generalizations drew on the earlier work of Wilhelm Steinitz, and were upheld by Tarrasch's sharp tongue when dismissing the opinions of doubters. While the greatest players of the time, among them Alekhine, Emanuel Lasker and Capablanca, clearly did not allow their play to be hobbled by blind adherence to general concepts that the center had to be controlled by pawns, that development had to happen in support of this control, that rooks always belong on open files, that wing openings were unsound—core ideas of Tarrasch's chess philosophy as popularly understood—beginners were taught to think of these generalizations as unalterable principles.

Nimzowitsch supplemented many of the earlier simplistic assumptions about chess strategy by enunciating in his turn a further number of general concepts of defensive play aimed at achieving one's own goals by preventing realization of the opponent's plans. Notable in his "system" were concepts such as overprotection of pieces and pawns under attack, control of the center by pieces instead of pawns, blockading of opposing pieces (notably the passed pawns) and prophylaxis. His aforementioned game versus Paul Johner in 1926 (listed in the notable games below) is a great example of Nimzowitsch's concept of 'first restrain, then blockade and finally destroy'. He manoeuvres the black queen from its starting point to h7 to form a part of king-side blockade along with the knight on f6 and h-pawn to stop any attacking threats from White. He was also a leading exponent of the fianchetto development of bishops. Perhaps most importantly, he formulated the terminology still in use for various complex chess strategies. Others had used these ideas in practice, but he was the first to present them systematically as a lexicon of themes accompanied by extensive taxonomical observations.

Raymond Keene writes that Nimzowitsch "was one of the world's leading grandmasters for a period extending over a quarter of a century, and for some of that time he was the obvious challenger for the world championship. ... [He was also] a great and profound chess thinker second only to Steinitz, and his works – Die Blockade, My System and Chess Praxis – established his reputation as one of the father figures of modern chess." GM Robert Byrne called him "perhaps the most brilliant theoretician and teacher in the history of the game." GM Jan Hein Donner called Nimzowitsch "a man who was too much of an artist to be able to prove he was right and who was regarded as something of a madman in his time. He would be understood only long after his death."

Many chess openings and variations are named after Nimzowitsch, the most famous being the Nimzo-Indian Defence (1.d4 Nf6 2.c4 e6 3.Nc3 Bb4) and the less often played Nimzowitsch Defence (1.e4 Nc6). Nimzowitsch biographer GM Raymond Keene and others have referred to 1.Nf3 followed by 2.b3 as the Nimzowitsch–Larsen Attack. Keene wrote a book about the opening with that title. These openings all exemplify Nimzowitsch's ideas about controlling the center with pieces instead of pawns. He was also vital in the development of two important systems in the French Defence, the Winawer Variation (in some places called the Nimzowitsch Variation; its moves are 1.e4 e6 2.d4 d5 3.Nc3 Bb4) and the Advance Variation (1.e4 e6 2.d4 d5 3.e5). He also pioneered two provocative variations of the Sicilian Defence: the Nimzowitsch Variation, 1.e4 c5 2.Nf3 Nf6, which invites 3.e5 Nd5 (similar to Alekhine's Defence) and 1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 d5?! (the latter regarded as dubious today). International Master John L. Watson has dubbed the line 1.c4 Nf6 2.Nc3 e6 3.Nf3 Bb4 the "Nimzo-English", employing this designation in Chapter 11 of his book Mastering the Chess Openings, Volume 3.

Personality
There are many entertaining anecdotes regarding Nimzowitsch—some less savory than others. An article by Hans Kmoch and Fred Reinfeld entitled "Unconventional Surrender" on page 55 of the February 1950 Chess Review tells of the "... example of Nimzowitsch, who ... once missed first prize in a tournament in Berlin by losing to Sämisch, and when it became clear he was going to lose the game, Nimzowitsch stood up on the table and shouted, 'Gegen diesen Idioten muss ich verlieren!' ('I must lose to this idiot!')".

Nimzowitsch was annoyed by his opponents' smoking. A popular, but probably apocryphal, story is that once when an opponent laid an unlit cigar on the table, he complained to the tournament arbiters, "He is threatening to smoke, and as an old player you must know that the threat is stronger than the execution."

Nimzowitsch had lengthy and somewhat bitter dogmatic conflicts with Tarrasch over whose ideas constituted 'proper' chess.

Nimzowitsch's vanity and faith in his ideas of overprotection provoked Hans Kmoch to write a parody about him in February 1928 in the Wiener Schachzeitung. This consisted of a mock game against the fictional player "Systemsson", supposedly played and annotated by Nimzowitsch himself. The annotations gleefully exaggerate the idea of overprotection, as well as asserting the true genius of the wondrous idea. Kmoch was in fact a great admirer of Nimzowitsch, and Nimzowitsch was amused at the effort.

Kmoch also wrote an article about his nine years with Nimzowitsch: "Nimzovich suffered from the delusion that he was unappreciated and that the reason was malice. All it took to make him blossom, as I later learned, was a little praise. His paranoia was most evident when he dined in company. He always thought he was served much smaller portions than everyone else. He didn't care about the actual amount but only about the imagined affront. I once suggested that he and I order what the other actually wanted and, when the food was served, exchange plates. After we had done so, he shook his head in disbelief, still thinking that he had received the smaller portion."

Nimzowitsch's colleague Tartakower observed of him, "He pretends to be crazy in order to drive us all crazy."

Death
Although he had long suffered from heart trouble, his early death was unexpected; taken ill suddenly at the end of 1934, he lay bedridden for three months before dying of pneumonia. He is buried in Bispebjerg Cemetery in Copenhagen.

Notable games

 * Friedrich Sämisch vs Aron Nimzowitsch, Copenhagen 1923, 0–1 The "Immortal Zugzwang Game"
 * Paul Johner vs Aron Nimzowitsch, Dresden 1926, 0–1 This game was chosen by Bent Larsen as his favourite game in Learn from the Grandmasters.
 * Richard Réti vs Aron Nimzowitsch, Berlin 1928, 0–1
 * Efim Bogoljubov vs Aron Nimzowitsch, San Remo 1930, 0–1

title: Aron Nimzowitsch


text:
Aragonese language

Aragonese (aragonés in Aragonese) is a Romance language spoken in several dialects by about 12,000 people as of 2011, in the Pyrenees valleys of Aragon, Spain, primarily in the comarcas of Somontano de Barbastro, Jacetania, Alto Gállego, Sobrarbe, and Ribagorza/Ribagorça. It is the only modern language which survived from medieval Navarro-Aragonese in a form distinct from Spanish.

Historically, people referred to the language as fabla ('talk' or 'speech'). Native Aragonese people usually refer to it by the names of its local dialects such as cheso (from Valle de Hecho) or patués (from the Benasque Valley).

History

Aragonese, which developed in portions of the Ebro basin, can be traced back to the High Middle Ages. It spread throughout the Pyrenees to areas where languages similar to modern Basque might have been previously spoken. The Kingdom of Aragon (formed by the counties of Aragon, Sobrarbe and Ribagorza) expanded southward from the mountains, pushing the Moors farther south in the Reconquista and spreading the Aragonese language.

The union of the Catalan counties and the Kingdom of Aragon which formed the 12th-century Crown of Aragon did not merge the languages of the two territories; Catalan continued to be spoken in the east and Navarro-Aragonese in the west, with the boundaries blurred by dialectal continuity. The Aragonese Reconquista in the south ended with the cession of Murcia by James I of Aragon to the Kingdom of Castile as dowry for an Aragonese princess.

The best-known proponent of the Aragonese language was Johan Ferrandez d'Heredia, the Grand Master of the Knights Hospitaller in Rhodes at the end of the 14th century. He wrote an extensive catalog of works in Aragonese and translated several works from Greek into Aragonese (the first in medieval Europe).

The spread of Castilian (Spanish), the Castilian origin of the Trastámara dynasty, and the similarity between Castilian (Spanish) and Aragonese facilitated the recession of the latter. A turning point was the 15th-century coronation of the Castilian Ferdinand I of Aragon, also known as Ferdinand of Antequera.

In the early 18th century, after the defeat of the allies of Aragon in the War of the Spanish Succession, Philip V ordered the prohibition of the Aragonese language in schools and the establishment of Castilian (Spanish) as the only official language in Aragon. This was ordered in the Aragonese Nueva Planta decrees of 1707.

In recent times, Aragonese was mostly regarded as a group of rural dialects of Spanish. Compulsory education undermined its already weak position; for example, pupils were punished for using it. However, the 1978 Spanish transition to democracy heralded literary works and studies of the language.

Modern Aragonese
Aragonese is the native language of the Aragonese mountain ranges of the Pyrenees, in the comarcas of Somontano, Jacetania, Sobrarbe, and Ribagorza. Cities and towns in which Aragonese is spoken are Huesca, Graus, Monzón, Barbastro, Bielsa, Chistén, Fonz, Echo, Estadilla, Benasque, Campo, Sabiñánigo, Jaca, Plan, Ansó, Ayerbe, Broto, and El Grado.

It is spoken as a second language by inhabitants of Zaragoza, Huesca, Ejea de los Caballeros, or Teruel. According to recent polls, there are about 25,500 speakers (2011) including speakers living outside the native area. In 2017, the Dirección General de Política Lingüística de Aragón estimated there were 10,000 to 12,000 active speakers of Aragonese.

In 2009, the Languages Act of Aragon (Law 10/2009) recognized the "native language, original and historic" of Aragon. The language received several linguistic rights, including its use in public administration. Some of the legislation was repealed by a new law in 2013 (Law 3/2013). [See Languages Acts of Aragon for more information on the subject]

Dialects

 * Western dialect: Ansó, Valle de Hecho, Chasa, Berdún, Chaca
 * Central dialect: Panticosa, Biescas, Torla, Broto, Bielsa, Yebra de Basa, Aínsa-Sobrarbe
 * Eastern dialect: Benás, Plan, Bisagorri, Campo, Perarrúa, Graus, Estadilla
 * Southern dialect: Agüero, Ayerbe, Rasal, Bolea, Lierta, Uesca, Almudévar, Nozito, Labata, Alguezra, Angüés, Pertusa, Balbastro, Nabal

Traits
Aragonese has many historical traits in common with Catalan. Some are conservative features that are also shared with the Asturleonese languages and Galician–Portuguese, where Spanish innovated in ways that did not spread to nearby languages.

Shared with Catalan

 * Romance initial f- is preserved, e.g. filium > fillo ('son', Sp. hijo, Cat. fill, Pt. filho).
 * Romance groups cl-, fl- and pl- are preserved and in most dialects do not undergo any change, e.g. clavis > clau ('key', Sp. llave, Cat. clau, Pt. chave). However, in some transitional dialects from both sides (Ribagorzano in Aragonese and Ribagorçà and Pallarès in Catalan) it becomes cll-, fll- and pll-, e.g. clavis > cllau.
 * Romance palatal approximant (ge-, gi-, i-) consistently became medieval, as in medieval Catalan and Portuguese. This becomes modern ch , as a result of the devoicing of sibilants (see below). In Spanish, the medieval result was either /, (modern ), , or nothing, depending on the context. e.g. iuvenem > choven ('young man', Sp. joven , Cat. jove ), gelare > chelar ('to freeze', Sp. helar , Cat. gelar ).
 * Romance groups -lt-, -ct- result in, e.g. factum > feito ('done', Sp. hecho, Cat. fet, Gal./Port. feito), multum > muito ('many, much', Sp. mucho, Cat. molt, Gal. moito, Port. muito).
 * Romance groups -x-, -ps-, scj- result in voiceless palatal fricative ix, e.g. coxu > coixo ('crippled', Sp. cojo, Cat. coix).
 * Romance groups -lj-, -c'l-, -t'l- result in palatal lateral ll, e.g. muliere > muller ('woman', Sp. mujer, Cat. muller), acuc'la > agulla ('needle', Sp. aguja, Cat. agulla).

Shared with Catalan and Spanish

 * Open o, e from Romance result systematically in diphthongs, , e.g. vet'la > viella ('old woman', Sp. vieja, Cat. vella, Pt. velha). This includes before a palatal approximant, e.g. octō > ueito ('eight', Sp. ocho, Cat. vuit, Pt. oito). Spanish diphthongizes except before yod, whereas Catalan only diphthongizes before yod.
 * Voiced stops may be lenited to approximants.

Shared with Spanish

 * Loss of final unstressed -e but not -o, e.g. grande > gran ('big'), factum > feito ('done'). Catalan loses both -e and -o (Cat. gran, fet); Spanish preserves -o and sometimes -e (Sp. hecho, gran ~ grande).
 * Former voiced sibilants become voiceless.
 * The palatal is most often realized as a fricative.

Shared with neither

 * Latin -b- is maintained in past imperfect endings of verbs of the second and third conjugations: teneba, teniba ('he had', Sp. tenía, Cat. tenia), dormiba ('he was sleeping', Sp. dormía, Cat. dormia).
 * High Aragonese dialects (alto aragonés) and some dialects of Gascon have preserved the voicelessness of many intervocalic stop consonants, e.g. cletam > cleta ('sheep hurdle', Cat. cleda, Fr. claie), cuculliatam > cocullata ('crested lark', Sp. cogujada, Cat. cogullada).
 * Several Aragonese dialects maintain Latin -ll- as geminate.
 * The mid vowels can be as open as, mainly in the Benasque dialect.
 * No native word can begin with an, a trait shared with Gascon and Basque.

Orthography
Before 2023, Aragonese had three orthographic standards:
 * The grafía de Uesca, codified in 1987 by the Consello d'a Fabla Aragonesa (CFA) at a convention in Huesca, is used by most Aragonese writers. It has a more uniform system of assigning letters to phonemes, with less regard for etymology; words traditionally written with $⟨v⟩$ and $⟨b⟩$ are uniformly written with $⟨b⟩$ in the Uesca system. Similarly, $⟨ch⟩$, $⟨j⟩$, and $⟨g⟩$ before $⟨e⟩$ and $⟨i⟩$ are all written $⟨ch⟩$. It uses letters associated with Spanish, such as $⟨ñ⟩$.
 * The grafia SLA, devised in 2004 by the Sociedat de Lingüistica Aragonesa (SLA), is used by some Aragonese writers. It uses etymological forms which are closer to Catalan, Occitan, and medieval Aragonese sources; trying to come closer to the original Aragonese and the other Occitano-Romance languages. In the SLA system $⟨v⟩$, $⟨b⟩$,$⟨ch⟩$, $⟨j⟩$, and $⟨g⟩$ before $⟨e⟩$ and $⟨i⟩$ are distinct, and the digraph $⟨ny⟩$ replaces $⟨ñ⟩$.
 * In 2010, the Academia de l'Aragonés (founded in 2006) established an orthographic standard to modernize medieval orthography and to make it more etymological.

During the 16th century, Aragonese Moriscos wrote aljamiado texts (Romance texts in Arabic script), possibly because of their inability to write in Arabic. The language in these texts has a mixture of Aragonese and Castilian traits, and they are among the last known written examples of the Aragonese formerly spoken in central and southern Aragon.

In 2023, a new orthographic standard has been published by the Academia Aragonesa de la Lengua. This version is close to the Academia de l'Aragonés orthography, but with the following differences: is always spelled ⟨cu⟩, e. g. cuan, cuestión (exception is made for some loanwords: quad, quadrívium, quark, quásar, quáter, quórum);  is spelled ⟨ny⟩ or ⟨ñ⟩ by personal preference; final ⟨z⟩ is not written as ⟨tz⟩.

The marginal phoneme (only in loanwords, e. g. jabugo) is spelled j in the Uesca, Academia de l'Aragonés and Academia Aragonesa de la Lengua standards (not mentioned in the SLA standard). Additionally, the Academia de l'Aragonés and Academia Aragonesa de la Lengua orthographies allow the letter j in some loanwords internationally known with it (e. g. jazz, jacuzzi, which normally have in the Aragonese pronunciation) and also mention the letters k and w, also used only in loanwords (w may represent  or ).

Grammar
Aragonese grammar has a lot in common with Occitan and Catalan, but also Spanish.

Articles
The definite article in Aragonese has undergone dialect-related changes, with definite articles in Old Aragonese similar to their present Spanish equivalents. There are two main forms: These forms are used in the eastern and some central dialects.

These forms are used in the western and some central dialects.

Lexicology
Neighboring Romance languages have influenced Aragonese. Catalan and Occitan influenced Aragonese for many years. Since the 15th century, Spanish has most influenced Aragonese; it was adopted throughout Aragon as the first language, limiting Aragonese to the northern region surrounding the Pyrenees. French has also influenced Aragonese; Italian loanwords have entered through other languages (such as Catalan), and Portuguese words have entered through Spanish. Germanic words came with the conquest of the region by Germanic peoples during the fifth century, and English has introduced a number of new words into the language.

Gender
Words that were part of the Latin second declension—as well as words that joined it later on—are usually masculine:

 * filiu(m) > fillo ('son')
 * sciuru + olu(m) > esquiruelo, esquirol ('squirrel')

Words that were part of the Latin first declension are usually feminine:
 * filia(m) > filla ('daughter').

Some Latin neuter plural nouns joined the first declension as singular feminine nouns:
 * folia > fuella ('leaf').

Words ending in -or are feminine:
 * a honor, a calor, a color, and (in Medieval Aragonese) la amor

The names of fruit trees usually end in -era (a suffix derived from Latin -aria) and are usually feminine:
 * a perera, a manzanera, a nuquera, a castanyera, a tellera / o tilero, a olivera, a ciresera, l'almendrera

The genders of river names vary:

 * Many ending in -a are feminine: a Cinca/a Cinga, a Cinqueta, a Garona, L'Arba, a Noguera, a Isuela, La Uecha, La Uerva, etc. The last was known as río de la Uerba during the 16th century.
 * Many from the second and the third declension are masculine: L'Ebro, O Galligo, O Flumen, L'Alcanadre.

Pronouns
Just like most other Occitano-Romance languages, Aragonese has partitive and locative clitic pronouns derived from the Latin inde and ibi: en/ne and bi/i/ie; unlike Ibero-Romance.

Such pronouns are present in most major Romance languages (Catalan en and hi, Occitan ne and i, French en and y, and Italian ne and ci/vi).

En/ne is used for:
 * Partitive objects: No n'he visto como aquello ("I haven't seen anything like that", literally 'Not (of it) I have seen like that').
 * Partitive subjects: En fa tanto de mal ("It hurts so much", literally '(of it) it causes so much of pain')
 * Ablatives, places from which movements originate: Se'n va ra memoria ("Memory goes away", literally '(away from [the mind]) memory goes')

Bi/hi/ie is used for:
 * Locatives, where something takes place: N'hi heba uno ("There was one of them"), literally '(Of them) there was one')
 * Allatives, places that movements go towards or end: Vés-be ('Go there (imperative)')

Literature
Aragonese was not written until the 12th and 13th centuries; the history Liber Regum, Razón feita d'amor, Libre dels tres reys d'orient, and Vida de Santa María Egipcíaca date from this period; there is also an Aragonese version of the Chronicle of the Morea, differing also in its content and written in the late 14th century called Libro de los fechos et conquistas del principado de la Morea.

Early modern period
Since 1500, Spanish has been the cultural language of Aragon; many Aragonese wrote in Spanish, and during the 17th century the Argensola brothers went to Castile to teach Spanish. Aragonese became a popular village language. During the 17th century, popular literature in the language began to appear. In a 1650 Huesca literary contest, Aragonese poems were submitted by Matías Pradas, Isabel de Rodas and "Fileno, montañés".

Contemporary literature
The 19th and 20th centuries have seen a renaissance of Aragonese literature in several dialects. In 1844, Braulio Foz's novel Vida de Pedro Saputo was published in the Almudévar (southern) dialect. The 20th century featured Domingo Miral's costumbrist comedies and Veremundo Méndez Coarasa's poetry, both in Hecho (western) Aragonese; Cleto Torrodellas' poetry and Tonón de Baldomera's popular writings in the Graus (eastern) dialect and Arnal Cavero's costumbrist stories and Juana Coscujuela's novel A Lueca, historia d'una moceta d'o Semontano, also in the southern dialect.

Aragonese in modern education
The 1997 Aragonese law of languages stipulated that Aragonese (and Catalan) speakers had a right to the teaching of and in their own language. Following this, Aragonese lessons started in schools in the 1997–1998 academic year. It was originally taught as an extra-curricular, non-evaluable voluntary subject in four schools. However, whilst legally schools can choose to use Aragonese as the language of instruction, as of the 2013–2014 academic year, there are no recorded instances of this option being taken in primary or secondary education. In fact, the only current scenario in which Aragonese is used as the language of instruction is in the Aragonese philology university course, which is optional, taught over the summer and in which only some of the lectures are in Aragonese.

Pre-school education
In pre-school education, students whose parents wish them to be taught Aragonese receive between thirty minutes to one hour of Aragonese lessons a week. In the 2014–2015 academic year there were 262 students recorded in pre-school Aragonese lessons.

Primary school education
The subject of Aragonese now has a fully developed curriculum in primary education in Aragon. Despite this, in the 2014–2015 academic year there were only seven Aragonese teachers in the region across both pre-primary and primary education and none hold permanent positions, whilst the number of primary education students receiving Aragonese lessons was 320.

As of 2017 there were 1068 reported Aragonese language students and 12 Aragonese language instructors in Aragon.

Secondary school education
There is no officially approved program or teaching materials for the Aragonese language at the secondary level, and though two non-official textbooks are available (Pos ixo... Materials ta aprender aragonés (Benítez, 2007) and Aragonés ta Secundaria (Campos, 2014)) many instructors create their own learning materials. Further, most schools with Aragonese programs that have the possibility of being offered as an examinative subject have elected not to do so.

As of 2007 it is possible to use Aragonese as a language of instruction for multiple courses; however, no program is yet to instruct any curricular or examinative courses in Aragonese. As of the 2014–2015 academic year there were 14 Aragonese language students at the secondary level.

Higher education
Aragonese is not currently a possible field of study for a bachelor's or postgraduate degree in any official capacity, nor is Aragonese used as a medium of instruction. A bachelor's or master's degree may be obtained in Magisterio (teaching) at the University of Zaragoza; however, no specialization in Aragonese language is currently available. As such those who wish to teach Aragonese at the pre-school, primary, or secondary level must already be competent in the language by being a native speaker or by other means. Further, prospective instructors must pass an ad hoc exam curated by the individual schools at which they wish to teach in order to prove their competence, as there are no recognized standard competency exams for the Aragonese language.

Since the 1994–1995 academic year, Aragonese has been an elective subject within the bachelor's degree for primary school education at the University of Zaragoza's Huesca campus.

The University of Zaragoza's Huesca campus also offers a Diploma de Especialización (These are studies that require a previous university degree and have a duration of between 30 and 59 ECTS credits.) in Aragonese Philology with 37 ECTS credits.

 * Academia de l'Aragonés
 * Arredol – Electronic Aragonese newspaper
 * Rosario Ustáriz Borra

title: Aragonese language


text:
Advanced Mobile Phone System

Advanced Mobile Phone System (AMPS) was an analog mobile phone system standard originally developed by Bell Labs and later modified in a cooperative effort between Bell Labs and Motorola. It was officially introduced in the Americas on October 13, 1983,  and was deployed in many other countries too, including Israel in 1986, Australia in 1987, Singapore in 1988, and Pakistan in 1990. It was the primary analog mobile phone system in North America (and other locales) through the 1980s and into the 2000s. As of February 18, 2008, carriers in the United States were no longer required to support AMPS and companies such as AT&T and Verizon Communications have discontinued this service permanently. AMPS was discontinued in Australia in September 2000, in India by October 2004, in Israel by January 2010, and Brazil by 2010.

History
The first cellular network efforts began at Bell Labs and with research conducted at Motorola. In 1960, John F. Mitchell became Motorola's chief engineer for its mobile-communication products, and oversaw the development and marketing of the first pager to use transistors.

Motorola had long produced mobile telephones for automobiles, but these large and heavy models consumed too much power to allow their use without the automobile's engine running. Mitchell's team, which included Dr. Martin Cooper, developed portable cellular telephony. Cooper and Mitchell were among the Motorola employees granted a patent for this work in 1973. The first call on the prototype connected, reportedly, to a wrong number.

While Motorola was developing a cellular phone, from 1968 to 1983 Bell Labs worked out a system called Advanced Mobile Phone System (AMPS), which became the first cellular network standard in the United States. The first system was successfully deployed in Chicago, Illinois, in 1979. Motorola and others designed and built the cellular phones for this and other cellular systems. Louis M. Weinberg, a marketing director at AT&T, was named the first president of the AMPS corporation. He served in this position during the startup of the AMPS subsidiary of AT&T.

Martin Cooper, a former general manager for the systems division at Motorola, led a team that produced the first cellular handset in 1973 and made the first phone call from it. In 1983 Motorola introduced the DynaTAC 8000x, the first commercially available cellular phone small enough to be easily carried. He later introduced the so-called Bag Phone.

In 1992, the first smartphone, called IBM Simon, used AMPS. Frank Canova led its design at IBM and it was demonstrated that year at the COMDEX computer-industry trade-show. A refined version of the product was marketed to consumers in 1994 by BellSouth under the name Simon Personal Communicator. The Simon was the first device that can be properly referred to as a "smartphone", even though that term was not yet coined.

Technology
AMPS is a first-generation cellular technology that uses separate frequencies, or "channels", for each conversation. It therefore required considerable bandwidth for a large number of users. In general terms, AMPS was very similar to the older "0G" Improved Mobile Telephone Service it replaced, but used considerably more computing power to select frequencies, hand off conversations to land lines, and handle billing and call setup.

What really separated AMPS from older systems is the "back end" call setup functionality. In AMPS, the cell centers could flexibly assign channels to handsets based on signal strength, allowing the same frequency to be re-used, without interference, if locations were separated enough. The channels were grouped so a specific set was different of the one used on the cell nearby. This allowed a larger number of phones to be supported over a geographical area. AMPS pioneers coined the term "cellular" because of its use of small hexagonal "cells" within a system.

AMPS suffered from many weaknesses compared to today's digital technologies. As an analog standard, it was susceptible to static and noise, and there was no protection from 'eavesdropping' using a scanner or an older TV set that could tune into channels 70-83.

Cloning
In the 1990s, an epidemic of "cloning" cost the cellular carriers millions of dollars. An eavesdropper with specialized equipment could intercept a handset's ESN (Electronic Serial Number) and MDN or CTN (Mobile Directory Number or Cellular Telephone Number). The Electronic Serial Number, a 12-digit number sent by the handset to the cellular system for billing purposes, uniquely identified that phone on the network. The system then allowed or disallowed calls and/or features based on its customer file. A person intercepting an ESN/MDN pair could clone the combination onto a different phone and use it in other areas for making calls without paying.

Cellular phone cloning became possible with off-the-shelf technology in the 1990s. Would-be cloners required three key items :

 * 1) A radio receiver, such as the Icom PCR-1000, that could tune into the Reverse Channel (the frequency on which AMPS phones transmit data to the tower)
 * 2) A PC with a sound card and a software program called Banpaia
 * 3) A phone that could easily be used for cloning, such as the Oki 900

The radio, when tuned to the proper frequency, would receive the signal transmitted by the cell phone to be cloned, containing the phone's ESN/MDN pair. This signal would feed into the sound-card audio-input of the PC, and Banpaia would decode the ESN/MDN pair from this signal and display it on the screen. The hacker could then copy that data into the Oki 900 phone and reboot it, after which the phone network could not distinguish the Oki from the original phone whose signal had been received. This gave the cloner, through the Oki phone, the ability to use the mobile-phone service of the legitimate subscriber whose phone was cloned – just as if that phone had been physically stolen, except that the subscriber retained his or her phone, unaware that the phone had been cloned—at least until that subscriber received his or her next bill.

The problem became so large that some carriers required the use of a PIN before making calls. Eventually, the cellular companies initiated a system called RF Fingerprinting, whereby it could determine subtle differences in the signal of one phone from another and shut down some cloned phones. Some legitimate customers had problems with this though if they made certain changes to their own phone, such as replacing the battery and/or antenna.

The Oki 900 could listen in to AMPS phone-calls right out-of-the-box with no hardware modifications.

Standards
AMPS was originally standardized by American National Standards Institute (ANSI) as EIA/TIA/IS-3. EIA/TIA/IS-3 was superseded by EIA/TIA-553 and TIA interim standard with digital technologies, the cost of wireless service is so low that the problem of cloning has virtually disappeared.

Frequency bands
AMPS cellular service operated in the 850 MHz Cellular band. For each market area, the United States Federal Communications Commission (FCC) allowed two licensees (networks) known as "A" and "B" carriers. Each carrier within a market used a specified "block" of frequencies consisting of 21 control channels and 395 voice channels. Originally, the B (wireline) side license was usually owned by the local phone company, and the A (non-wireline) license was given to wireless telephone providers.

At the inception of cellular in 1983, the FCC had granted each carrier within a market 333 channel pairs (666 channels total). By the late 1980s, the cellular industry's subscriber base had grown into the millions across America and it became necessary to add channels for additional capacity. In 1989, the FCC granted carriers an expansion from the previous 666 channels to the final 832 (416 pairs per carrier). The additional frequencies were from the band held in reserve for future (inevitable) expansion. These frequencies were immediately adjacent to the existing cellular band. These bands had previously been allocated to UHF TV channels 70–83.

Each duplex channel was composed of 2 frequencies. 416 of these were in the 824–849 MHz range for transmissions from mobile stations to the base stations, paired with 416 frequencies in the 869–894 MHz range for transmissions from base stations to the mobile stations. Each cell site used a different subset of these channels than its neighbors to avoid interference. This significantly reduced the number of channels available at each site in real-world systems. Each AMPS channel had a one way bandwidth of 30 kHz, for a total of 60 kHz for each duplex channel.

Laws were passed in the US which prohibited the FCC type acceptance and sale of any receiver which could tune the frequency ranges occupied by analog AMPS cellular services. Though the service is no longer offered, these laws remain in force (although they may no longer be enforced).

Narrowband AMPS
In 1991, Motorola proposed an AMPS enhancement known as narrowband AMPS (NAMPS or N-AMPS).

Digital AMPS
Later, many AMPS networks were partially converted to D-AMPS, often referred to as TDMA (though TDMA is a generic term that applies to many 2G cellular systems). D-AMPS, commercially deployed since 1993, was a digital, 2G standard used mainly by AT&T Mobility and U.S. Cellular in the United States, Rogers Wireless in Canada, Telcel in Mexico, Telecom Italia Mobile (TIM) in Brazil, VimpelCom in Russia, Movilnet in Venezuela, and Cellcom in Israel. In most areas, D-AMPS is no longer offered and has been replaced by more advanced digital wireless networks.

Successor technologies
AMPS and D-AMPS have now been phased out in favor of either CDMA2000 or GSM, which allow for higher capacity data transfers for services such as WAP, Multimedia Messaging System (MMS), and wireless Internet access. There are some phones capable of supporting AMPS, D-AMPS and GSM all in one phone (using the GAIT standard).

Analog AMPS being replaced by digital
In 2002, the FCC decided to no longer require A and B carriers to support AMPS service as of February 18, 2008. All AMPS carriers have converted to a digital standard such as CDMA2000 or GSM. Digital technologies such as GSM and CDMA2000 support multiple voice calls on the same channel and offer enhanced features such as two-way text messaging and data services.

Unlike in the United States, the Canadian Radio-television and Telecommunications Commission (CRTC) and Industry Canada have not set any requirement for maintaining AMPS service in Canada. Rogers Wireless has dismantled their AMPS (along with IS-136) network; the networks were shut down May 31, 2007. Bell Mobility and Telus Mobility, who operated AMPS networks in Canada, announced that they would observe the same timetable as outlined by the FCC in the United States, and as a result would not begin to dismantle their AMPS networks until after February 2008.

OnStar relied heavily on North American AMPS service for its subscribers because, when the system was developed, AMPS offered the most comprehensive wireless coverage in the US. In 2006, ADT asked the FCC to extend the AMPS deadline due to many of their alarm systems still using analog technology to communicate with the control centers. Cellular companies who own an A or B license (such as Verizon and Alltel) were required to provide analog service until February 18, 2008. After that point, however, most cellular companies were eager to shut down AMPS and use the remaining channels for digital services. OnStar transitioned to digital service with the help of data transport technology developed by Airbiquity, but warned customers who could not be upgraded to digital service that their service would permanently expire on January 1, 2008.

title: Advanced Mobile Phone System


text:
Aerodynamics

 Aerodynamics (ἀήρ aero (air) + δυναμική (dynamics)) is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dynamics and its subfield of gas dynamics, and is an important domain of study in aeronautics. The term aerodynamics is often used synonymously with gas dynamics, the difference being that "gas dynamics" applies to the study of the motion of all gases, and is not limited to air. The formal study of aerodynamics began in the modern sense in the eighteenth century, although observations of fundamental concepts such as aerodynamic drag were recorded much earlier. Most of the early efforts in aerodynamics were directed toward achieving heavier-than-air flight, which was first demonstrated by Otto Lilienthal in 1891. Since then, the use of aerodynamics through mathematical analysis, empirical approximations, wind tunnel experimentation, and computer simulations has formed a rational basis for the development of heavier-than-air flight and a number of other technologies. Recent work in aerodynamics has focused on issues related to compressible flow, turbulence, and boundary layers and has become increasingly computational in nature.

History
Modern aerodynamics only dates back to the seventeenth century, but aerodynamic forces have been harnessed by humans for thousands of years in sailboats and windmills, and images and stories of flight appear throughout recorded history, such as the Ancient Greek legend of Icarus and Daedalus. Fundamental concepts of continuum, drag, and pressure gradients appear in the work of Aristotle and Archimedes.

In 1726, Sir Isaac Newton became the first person to develop a theory of air resistance, making him one of the first aerodynamicists. Dutch-Swiss mathematician Daniel Bernoulli followed in 1738 with Hydrodynamica in which he described a fundamental relationship between pressure, density, and flow velocity for incompressible flow known today as Bernoulli's principle, which provides one method for calculating aerodynamic lift. In 1757, Leonhard Euler published the more general Euler equations which could be applied to both compressible and incompressible flows. The Euler equations were extended to incorporate the effects of viscosity in the first half of the 1800s, resulting in the Navier–Stokes equations. The Navier–Stokes equations are the most general governing equations of fluid flow but are difficult to solve for the flow around all but the simplest of shapes.

In 1799, Sir George Cayley became the first person to identify the four aerodynamic forces of flight (weight, lift, drag, and thrust), as well as the relationships between them, and in doing so outlined the path toward achieving heavier-than-air flight for the next century. In 1871, Francis Herbert Wenham constructed the first wind tunnel, allowing precise measurements of aerodynamic forces. Drag theories were developed by Jean le Rond d'Alembert, Gustav Kirchhoff, and Lord Rayleigh. In 1889, Charles Renard, a French aeronautical engineer, became the first person to reasonably predict the power needed for sustained flight. Otto Lilienthal, the first person to become highly successful with glider flights, was also the first to propose thin, curved airfoils that would produce high lift and low drag. Building on these developments as well as research carried out in their own wind tunnel, the Wright brothers flew the first powered airplane on December 17, 1903.

During the time of the first flights, Frederick W. Lanchester, Martin Kutta, and Nikolai Zhukovsky independently created theories that connected circulation of a fluid flow to lift. Kutta and Zhukovsky went on to develop a two-dimensional wing theory. Expanding upon the work of Lanchester, Ludwig Prandtl is credited with developing the mathematics behind thin-airfoil and lifting-line theories as well as work with boundary layers.

As aircraft speed increased designers began to encounter challenges associated with air compressibility at speeds near the speed of sound. The differences in airflow under such conditions lead to problems in aircraft control, increased drag due to shock waves, and the threat of structural failure due to aeroelastic flutter. The ratio of the flow speed to the speed of sound was named the Mach number after Ernst Mach who was one of the first to investigate the properties of the supersonic flow. Macquorn Rankine and Pierre Henri Hugoniot independently developed the theory for flow properties before and after a shock wave, while Jakob Ackeret led the initial work of calculating the lift and drag of supersonic airfoils. Theodore von Kármán and Hugh Latimer Dryden introduced the term transonic to describe flow speeds between the critical Mach number and Mach 1 where drag increases rapidly. This rapid increase in drag led aerodynamicists and aviators to disagree on whether supersonic flight was achievable until the sound barrier was broken in 1947 using the Bell X-1 aircraft.

By the time the sound barrier was broken, aerodynamicists' understanding of the subsonic and low supersonic flow had matured. The Cold War prompted the design of an ever-evolving line of high-performance aircraft. Computational fluid dynamics began as an effort to solve for flow properties around complex objects and has rapidly grown to the point where entire aircraft can be designed using computer software, with wind-tunnel tests followed by flight tests to confirm the computer predictions. Understanding of supersonic and hypersonic aerodynamics has matured since the 1960s, and the goals of aerodynamicists have shifted from the behaviour of fluid flow to the engineering of a vehicle such that it interacts predictably with the fluid flow. Designing aircraft for supersonic and hypersonic conditions, as well as the desire to improve the aerodynamic efficiency of current aircraft and propulsion systems, continues to motivate new research in aerodynamics, while work continues to be done on important problems in basic aerodynamic theory related to flow turbulence and the existence and uniqueness of analytical solutions to the Navier–Stokes equations.

Fundamental concepts
Understanding the motion of air around an object (often called a flow field) enables the calculation of forces and moments acting on the object. In many aerodynamics problems, the forces of interest are the fundamental forces of flight: lift, drag, thrust, and weight. Of these, lift and drag are aerodynamic forces, i.e. forces due to air flow over a solid body. Calculation of these quantities is often founded upon the assumption that the flow field behaves as a continuum. Continuum flow fields are characterized by properties such as flow velocity, pressure, density, and temperature, which may be functions of position and time. These properties may be directly or indirectly measured in aerodynamics experiments or calculated starting with the equations for conservation of mass, momentum, and energy in air flows. Density, flow velocity, and an additional property, viscosity, are used to classify flow fields.

Flow classification
Flow velocity is used to classify flows according to speed regime. Subsonic flows are flow fields in which the air speed field is always below the local speed of sound. Transonic flows include both regions of subsonic flow and regions in which the local flow speed is greater than the local speed of sound. Supersonic flows are defined to be flows in which the flow speed is greater than the speed of sound everywhere. A fourth classification, hypersonic flow, refers to flows where the flow speed is much greater than the speed of sound. Aerodynamicists disagree on the precise definition of hypersonic flow.

Compressible flow accounts for varying density within the flow. Subsonic flows are often idealized as incompressible, i.e. the density is assumed to be constant. Transonic and supersonic flows are compressible, and calculations that neglect the changes of density in these flow fields will yield inaccurate results.

Viscosity is associated with the frictional forces in a flow. In some flow fields, viscous effects are very small, and approximate solutions may safely neglect viscous effects. These approximations are called inviscid flows. Flows for which viscosity is not neglected are called viscous flows. Finally, aerodynamic problems may also be classified by the flow environment. External aerodynamics is the study of flow around solid objects of various shapes (e.g. around an airplane wing), while internal aerodynamics is the study of flow through passages inside solid objects (e.g. through a jet engine).

Continuum assumption
Unlike liquids and solids, gases are composed of discrete molecules which occupy only a small fraction of the volume filled by the gas. On a molecular level, flow fields are made up of the collisions of many individual of gas molecules between themselves and with solid surfaces. However, in most aerodynamics applications, the discrete molecular nature of gases is ignored, and the flow field is assumed to behave as a continuum. This assumption allows fluid properties such as density and flow velocity to be defined everywhere within the flow.

The validity of the continuum assumption is dependent on the density of the gas and the application in question. For the continuum assumption to be valid, the mean free path length must be much smaller than the length scale of the application in question. For example, many aerodynamics applications deal with aircraft flying in atmospheric conditions, where the mean free path length is on the order of micrometers and where the body is orders of magnitude larger. In these cases, the length scale of the aircraft ranges from a few meters to a few tens of meters, which is much larger than the mean free path length. For such applications, the continuum assumption is reasonable. The continuum assumption is less valid for extremely low-density flows, such as those encountered by vehicles at very high altitudes (e.g. 300,000 ft/90 km) or satellites in Low Earth orbit. In those cases, statistical mechanics is a more accurate method of solving the problem than is continuum aerodynamics. The Knudsen number can be used to guide the choice between statistical mechanics and the continuous formulation of aerodynamics.

Conservation laws
The assumption of a fluid continuum allows problems in aerodynamics to be solved using fluid dynamics conservation laws. Three conservation principles are used:
 * Conservation of mass: Conservation of mass requires that mass is neither created nor destroyed within a flow; the mathematical formulation of this principle is known as the mass continuity equation.
 * Conservation of momentum: The mathematical formulation of this principle can be considered an application of Newton's Second Law. Momentum within a flow is only changed by external forces, which may include both surface forces, such as viscous (frictional) forces, and body forces, such as weight. The momentum conservation principle may be expressed as either a vector equation or separated into a set of three scalar equations (x,y,z components).
 * Conservation of energy: The energy conservation equation states that energy is neither created nor destroyed within a flow, and that any addition or subtraction of energy to a volume in the flow is caused by heat transfer, or by work into and out of the region of interest.

Together, these equations are known as the Navier–Stokes equations, although some authors define the term to only include the momentum equation(s). The Navier–Stokes equations have no known analytical solution and are solved in modern aerodynamics using computational techniques. Because computational methods using high speed computers were not historically available and the high computational cost of solving these complex equations now that they are available, simplifications of the Navier–Stokes equations have been and continue to be employed. The Euler equations are a set of similar conservation equations which neglect viscosity and may be used in cases where the effect of viscosity is expected to be small. Further simplifications lead to Laplace's equation and potential flow theory. Additionally, Bernoulli's equation is a solution in one dimension to both the momentum and energy conservation equations.

The ideal gas law or another such equation of state is often used in conjunction with these equations to form a determined system that allows the solution for the unknown variables.

Branches of aerodynamics
Aerodynamic problems are classified by the flow environment or properties of the flow, including flow speed, compressibility, and viscosity. External aerodynamics is the study of flow around solid objects of various shapes. Evaluating the lift and drag on an airplane or the shock waves that form in front of the nose of a rocket are examples of external aerodynamics. Internal aerodynamics is the study of flow through passages in solid objects. For instance, internal aerodynamics encompasses the study of the airflow through a jet engine or through an air conditioning pipe.

Aerodynamic problems can also be classified according to whether the flow speed is below, near or above the speed of sound. A problem is called subsonic if all the speeds in the problem are less than the speed of sound, transonic if speeds both below and above the speed of sound are present (normally when the characteristic speed is approximately the speed of sound), supersonic when the characteristic flow speed is greater than the speed of sound, and hypersonic when the flow speed is much greater than the speed of sound. Aerodynamicists disagree over the precise definition of hypersonic flow; a rough definition considers flows with Mach numbers above 5 to be hypersonic.

The influence of viscosity on the flow dictates a third classification. Some problems may encounter only very small viscous effects, in which case viscosity can be considered to be negligible. The approximations to these problems are called inviscid flows. Flows for which viscosity cannot be neglected are called viscous flows.

Incompressible aerodynamics
An incompressible flow is a flow in which density is constant in both time and space. Although all real fluids are compressible, a flow is often approximated as incompressible if the effect of the density changes cause only small changes to the calculated results. This is more likely to be true when the flow speeds are significantly lower than the speed of sound. Effects of compressibility are more significant at speeds close to or above the speed of sound. The Mach number is used to evaluate whether the incompressibility can be assumed, otherwise the effects of compressibility must be included.

Subsonic flow
Subsonic (or low-speed) aerodynamics describes fluid motion in flows which are much lower than the speed of sound everywhere in the flow. There are several branches of subsonic flow but one special case arises when the flow is inviscid, incompressible and irrotational. This case is called potential flow and allows the differential equations that describe the flow to be a simplified version of the equations of fluid dynamics, thus making available to the aerodynamicist a range of quick and easy solutions.

In solving a subsonic problem, one decision to be made by the aerodynamicist is whether to incorporate the effects of compressibility. Compressibility is a description of the amount of change of density in the flow. When the effects of compressibility on the solution are small, the assumption that density is constant may be made. The problem is then an incompressible low-speed aerodynamics problem. When the density is allowed to vary, the flow is called compressible. In air, compressibility effects are usually ignored when the Mach number in the flow does not exceed 0.3 (about 335 feet (102 m) per second or 228 miles (366 km) per hour at 60 °F (16 °C)). Above Mach 0.3, the problem flow should be described using compressible aerodynamics.

Compressible aerodynamics
According to the theory of aerodynamics, a flow is considered to be compressible if the density changes along a streamline. This means that – unlike incompressible flow – changes in density are considered. In general, this is the case where the Mach number in part or all of the flow exceeds 0.3. The Mach 0.3 value is rather arbitrary, but it is used because gas flows with a Mach number below that value demonstrate changes in density of less than 5%. Furthermore, that maximum 5% density change occurs at the stagnation point (the point on the object where flow speed is zero), while the density changes around the rest of the object will be significantly lower. Transonic, supersonic, and hypersonic flows are all compressible flows.

Transonic flow
The term Transonic refers to a range of flow velocities just below and above the local speed of sound (generally taken as Mach 0.8–1.2). It is defined as the range of speeds between the critical Mach number, when some parts of the airflow over an aircraft become supersonic, and a higher speed, typically near Mach 1.2, when all of the airflow is supersonic. Between these speeds, some of the airflow is supersonic, while some of the airflow is not supersonic.

Supersonic flow
Supersonic aerodynamic problems are those involving flow speeds greater than the speed of sound. Calculating the lift on the Concorde during cruise can be an example of a supersonic aerodynamic problem.

Supersonic flow behaves very differently from subsonic flow. Fluids react to differences in pressure; pressure changes are how a fluid is "told" to respond to its environment. Therefore, since sound is, in fact, an infinitesimal pressure difference propagating through a fluid, the speed of sound in that fluid can be considered the fastest speed that "information" can travel in the flow. This difference most obviously manifests itself in the case of a fluid striking an object. In front of that object, the fluid builds up a stagnation pressure as impact with the object brings the moving fluid to rest. In fluid traveling at subsonic speed, this pressure disturbance can propagate upstream, changing the flow pattern ahead of the object and giving the impression that the fluid "knows" the object is there by seemingly adjusting its movement and is flowing around it. In a supersonic flow, however, the pressure disturbance cannot propagate upstream. Thus, when the fluid finally reaches the object it strikes it and the fluid is forced to change its properties – temperature, density, pressure, and Mach number—in an extremely violent and irreversible fashion called a shock wave. The presence of shock waves, along with the compressibility effects of high-flow velocity (see Reynolds number) fluids, is the central difference between the supersonic and subsonic aerodynamics regimes.

Hypersonic flow
In aerodynamics, hypersonic speeds are speeds that are highly supersonic. In the 1970s, the term generally came to refer to speeds of Mach 5 (5 times the speed of sound) and above. The hypersonic regime is a subset of the supersonic regime. Hypersonic flow is characterized by high temperature flow behind a shock wave, viscous interaction, and chemical dissociation of gas.

Associated terminology

The incompressible and compressible flow regimes produce many associated phenomena, such as boundary layers and turbulence.

Boundary layers
The concept of a boundary layer is important in many problems in aerodynamics. The viscosity and fluid friction in the air is approximated as being significant only in this thin layer. This assumption makes the description of such aerodynamics much more tractable mathematically.

Turbulence
In aerodynamics, turbulence is characterized by chaotic property changes in the flow. These include low momentum diffusion, high momentum convection, and rapid variation of pressure and flow velocity in space and time. Flow that is not turbulent is called laminar flow.

Engineering design
Aerodynamics is a significant element of vehicle design, including road cars and trucks where the main goal is to reduce the vehicle drag coefficient, and racing cars, where in addition to reducing drag the goal is also to increase the overall level of downforce. Aerodynamics is also important in the prediction of forces and moments acting on sailing vessels. It is used in the design of mechanical components such as hard drive heads. Structural engineers resort to aerodynamics, and particularly aeroelasticity, when calculating wind loads in the design of large buildings, bridges, and wind turbines.

The aerodynamics of internal passages is important in heating/ventilation, gas piping, and in automotive engines where detailed flow patterns strongly affect the performance of the engine.

Environmental design
Urban aerodynamics are studied by town planners and designers seeking to improve amenity in outdoor spaces, or in creating urban microclimates to reduce the effects of urban pollution. The field of environmental aerodynamics describes ways in which atmospheric circulation and flight mechanics affect ecosystems.

Aerodynamic equations are used in numerical weather prediction.

Ball-control in sports
Sports in which aerodynamics are of crucial importance include soccer, table tennis, cricket, baseball, and golf, in which most players can control the trajectory of the ball using the "Magnus effect".

title: Aerodynamics


text:
Andreas Schlüter

Andreas Schlüter (1659 – c. June 1714) was a German baroque sculptor and architect, active in the Holy Roman Empire of the German Nation, the Polish–Lithuanian Commonwealth, and the Russian Tsardom.

Biography
Andreas Schlüter was born probably in Hamburg. His early life is obscure as at least three different persons of that name are documented. The records of St. Michaelis Church, Hamburg show that an Andreas Schlüter, son of sculptor Gerhart Schlüter, had been baptized there on 22 May 1664. Documents from Danzig/Gdańsk (Royal Prussia) reported that an Andreas Schlüter (senior) had worked 1640–1652 in Danzig's Jopengasse lane (today's ulica Piwna). Possibly born in 1640, an Andres Schliter is recorded as apprentice on 9 May 1656 by the mason's guild. Other sources state 1659 as year of birth.

He probably did spend several years abroad as Journeyman. His first work, in 1675, may have been epitaphs of the Dukes Sambor and Mestwin in the dome of Pelplin monastery.

Schlüter's first known work was the decoration of the facade of the Danzig Royal Chapel, in 1681. He later created statues for King John III Sobieski's Wilanów Palace in Warsaw and sepulchral sculptures in Zhovkva. In 1689, he moved to Warsaw and made the pediment reliefs and sculptural work of Krasiński Palace.

Schlüter was invited to Berlin in 1694 by Eberhard von Danckelmann to work as court sculptor at the armory (Zeughaus) for Elector Frederick III. His sculpted decorations are a masterpiece of baroque expression and pathos. While the more visible reliefs on the outside had to praise fighting, the statues of dying warriors in the interior denounced war and gave an indication of his pacifist religious beliefs (he is said to have been a Mennonite). Travelling through Italy in 1696, he studied the work of masters like Michelangelo Buonarroti and Gian Lorenzo Bernini.

Schlüter also worked as an architect and built many state buildings in Berlin in his role as "Hofbaumeister" (Court Architect), which he lost when one tower showed signs of a weak fundament. He also served as director of the Prussian Academy of Arts from 1702 to 1704, after which he began concentrating on sculpting again, as "Hofbildhauer" (Court Sculptor). His most important equestrian sculpture is that of the "Great Elector", Frederick William of Brandenburg, cast in 1708 and placed at "Lange Brücke" near the Berlin City Palace, now situated in the honor court before Charlottenburg Palace.

The Berlin City Palace, and many of his works, were partially destroyed by bombing in World War II and by the subsequent Communist regime. A similar fate probably befell the Amber Room, made between 1701 and 1709, Schlüter's most famous work of architecture.

In 1713, Schlüter's fame brought him to work for Tsar Peter I of Russia in Saint Petersburg, where he died of an illness after creating several designs. Together with Johann Friedrich Braunstein, he designed the Grand Palace and Monplaisir Palace in Peterhof Palace Complex. Also the city's oldest building, Kikin Hall, and the reliefs at the Summer Palace are attributed to him. This way he became an important figure of Petrine Baroque.

Extant works

 * Facade of the Royal Chapel, Gdańsk, 1681
 * Sculptures on the facade of Wilanów Palace, Warsaw, after 1681
 * Sculptures on the pediment of Krasiński Palace, Warsaw, 1682–83, 1689–1693
 * Epitaph of Adam Zygmunt Konarski, St. Mary's Cathedral of the Assumption, Frombork near Gdańsk, after 1683
 * Altar and crucifix in church, Węgrów near Warsaw, 1688–1690
 * Altar in Czerniaków church, Warsaw, 1690
 * Portrait bishop Jan Małachowski in Wawel Cathedral, Kraków 1693
 * Aepulchral sculptures of the Sobieski family, Zhovkva near Lviv, 1692–93
 * Equestrian statue of Elector Frederick William, courtyard of Charlottenburg Palace, Berlin, 1689–1703, with a copy in the Berlin Bode-Museum
 * Sculptures on the facade of the Zeughaus in Berlin, 1695–1706
 * Berlin Palace, 1699–1706
 * Amber Room (reconstruction) in the Catherine Palace of Tsarskoye Selo near Saint Petersburg, 1701
 * Pulpit, St. Mary's Church, Berlin, 1703
 * Sarcophagi of Friedrich I and Sophia Charlotte, King and Queen in Prussia in the Berlin Cathedral

title: Andreas Schlüter