Wednesday, July 30, 2008
A strapdown system has a dynamic measurement range several hundred times that required by a gimbaled system. That is, it must integrate the vehicle's attitude changes in pitch, roll and yaw, as well as gross movements. Gimballed systems could usually do well with update rates of 50 to 60 updates per second. However, strapdown systems normally update about 2000 times per second. The higher rate is needed to keep the maximum angular measurement within a practical range for real rate gyros: about 4 milliradians. Most rate gyros are now laser interferometers.
The data updating algorithms ("direction cosines" or "quaternions") involved are too complex to be accurately performed except by digital electronics. However, digital computers are now so inexpensive and fast that rate gyro systems can now be practically used and mass-produced. The Apollo lunar module used a strapdown system in its backup Abort Guidance System (AGS).
Strapdown systems are nowadays commonly used in commercial and tactical applications (arcraft, missiles, etc). However they are still not widespread in applications where superb accuracy is required (like submarine navigation or strategic ICBM guidance).
Wednesday, July 23, 2008
From a technical perspective, a Transaction Processing System (or Transaction Processing Monitor) monitors transaction programs, a special kind of programs. The essence of a transaction program is that it manages data that must be left in a consistent state. E.g. if an electronic payment is made, the amount must be either both withdrawn from one account and added to the other, or none at all. In case of a failure preventing transaction completion, the partially executed transaction must be 'rolled back' by the TPS. While this type of integrity must be provided also for batch transaction processing, it is particularly important for online processing: if e.g. an airline seat reservation system is accessed by multiple operators, after an empty seat inquiry, the seat reservation data must be locked until the reservation is made, otherwise another user may get the impression a seat is still free while it is actually being booked at the time. Without proper transaction monitoring, double bookings may occur. Other transaction monitor functions include deadlock detection and resolution (deadlocks may be inevitable in certain cases of cross-dependence on data), and transaction logging (in 'journals') for 'forward recovery' in case of massive failures.
Transaction Processing is not limited to application programs. The 'journaled file system' provided with IBMs AIX Unix operating system employs similar techniques to maintain file system integrity, including a journal.
Wednesday, July 16, 2008
Inspired by McLuhan, Neil Postman founded the Program in Media Ecology at New York University in 1971. He described it as
Media ecology looks into the matter of how media of communication affect human perception, understanding, feeling, and value; and how our interaction with media facilitates or impedes our chances of survival. The word ecology implies the study of environments: their structure, content, and impact on people.
Thursday, July 10, 2008
Some object-oriented databases are designed to work well with object-oriented programming languages such as Python, Java, C#, Visual Basic .NET, C++ and Smalltalk. Others have their own programming languages. ODBMSs use exactly the same model as object-oriented programming languages.
Wednesday, July 02, 2008
E-mail spam slowly but exponentially grew for several decades to several billion messages a day. Spam has frustrated, confused, and annoyed e-mail users. Laws against spam have been sporadically implemented, with some being opt-out and others requiring opt in e-mail. The total volume of spam (over 100 billion emails per day as of April 2008) has leveled off slightly in recent years, and is no longer growing exponentially. The amount received by most e-mail users has decreased, mostly because of better filtering. About 80% of all spam is sent by fewer than 200 spammers. Botnets, networks of virus-infected computers, are used to send about 80% of spam. The cost of spam is borne mostly by the recipient, so it is a form of postage due advertising.
Tuesday, June 24, 2008
Many normal computer users are however still unfamiliar with the term, and most never use it. Instead, "computer virus" is incorrectly used in common parlance and even in the media to describe all kinds of malware, though not all malware are viruses.
Software is considered malware based on the perceived intent of the creator rather than any particular features. Malware includes computer viruses, worms, trojan horses, most rootkits, spyware, dishonest adware, and other malicious and unwanted software. In law, malware is sometimes known as a computer contaminant, for instance in the legal codes of California, West Virginia, and several other American states.
Wednesday, June 18, 2008
Wednesday, June 11, 2008
Tuesday, June 03, 2008
It is the applied science of equipment design intended to maximize productivity by reducing operator fatigue and discomfort. The field is also called biotechnology, human engineering, and human factors engineering. Ergonomic research is primarily performed by ergonomists who study human capabilities in relationship to their work demands. Information derived from ergonomists contributes to the design and evaluation of tasks, jobs, products, environments and systems in order to make them compatible with the needs, abilities and limitations of people.
Wednesday, May 28, 2008
Alternative terms for free software have been a controversial issue among free software users from the late 1990s onwards. Coined in 1983 by Richard Stallman, "free software" is used to describe software which can be used, modified, and redistributed with little or no restriction. These freedoms are formally described in The Free Software Definition, first published in February 1986.
Alternatives for "free software" were sought because some businesses were uncomfortable with the word "free"s association with the ideas of freedom/liberty. A second problem was that the "available at no cost" ambiguity of the word "free" was seen as discouraging business adoption. In a 1998 strategy session in California, "open-source software" was selected by Todd Anderson, Larry Augustin, Jon Hall, Sam Ockman, Christine Peterson, and Eric S. Raymond. Richard Stallman had not been invited. The session was arranged in reaction to Netscape's January 1998 announcement of a source code release for Navigator (as Mozilla). Those at the meeting described "open source" as a "replacement label" for free software and founded the Open Source Initiative to promote the term as part of "a marketing program for free software" . Stallman and others object to the term "open-source software" because it does not describe all of the freedoms associated with the free software definition.
Tuesday, May 20, 2008
Psychosynthesis departed from the empirical foundations of psychology in that it studied a person as a personality and a soul but Assagioli continued to insist that it was scientific. Assagioli developed therapeutic methods other than what was found in psychoanalysis. Although the unconscious is an important part of the theory, Assagioli was careful to maintain a balance with rational, conscious therapeutical work.
Tuesday, May 13, 2008
Wednesday, May 07, 2008
The New Mobility Agenda is an international institution which while virtual and an open collaborative was originally set up by an international working group meeting at the Abbey de Royaumont near Paris with the support of the OECD in Paris in 1974 to challenge old ideas and practices in the field of urban transport through a long term collaborative program of information exchange, education and peer support. The Agenda today draws together the experience, expertise and support of more than four thousand individuals and groups world wide in an open collaborative peer network. One of the original proponents of this approach, Professor Mikoto Usui then director of the OECD Development Centre, referred to it in the founding meeting at the “Abbé de Royaumont as an “invisible college”. Drawing together the experience and expertise of more than four thousand individuals and groups world wide, who are networked via a combination of websites, discussion groups and fora, and collaborative projects, the Agenda takes an approach to transportation planning, policy and practice that has gained considerable force over the last two decades -- provides a leading-edge alternative to earlier (20th century) methods of looking at and providing mobility for people and goods in cities. The Agenda has received prestigious awards for its contributions, including the Stockholm Environment Challenge Prize (2000) and the World Technology Environment Award (2002).
Tuesday, April 29, 2008
Cost overrun is defined as excess of actual cost over budget. Cost overrun is also sometimes called "cost escalation," "cost increase," or "budget overrun." However, cost escalation and increases do not necessarily result in cost overruns if cost escalation is included in the budget.
Cost overrun is common in infrastructure, building, and technology projects. One of the most comprehensive studies of cost overrun that exists found that 9 out of 10 projects had overrun, overruns of 50 to 100 percent were common, overrun was found in each of 20 nations and five continents covered by the study, and overrun had been constant for the 70 years for which data were available. For IT projects, an industry study by the Standish Group (2004) found that average cost overrun was 43 percent, 71 percent of projects were over budget, over time, and under scope, and total waste was estimated at US$55 billion per year in the US alone.
Tuesday, April 22, 2008
Although having its origins in the late 1780s or earlier, the global standardisation of containers and container handling equipment was one of the important innovations in 20th century logistics.
By the 1830s, railroads on several continents were carrying containers that could be transferred to trucks or ships, but these containers were invariably small by today's standards. Originally used for shipping coal on and off barges, 'loose boxes' were used to containerize coal from the late 1780s, on places like the Bridgewater Canal. By the 1840's, iron boxes were in use as well as wooden ones. The early 1900s saw the adoption of closed container boxes designed for movement between road and rail.
Tuesday, April 15, 2008
In databases, snapshot isolation is a guarantee that all reads made in a transaction will see a consistent snapshot of the database, and the transaction itself will successfully commit only if no updates it has made conflict with any concurrent updates made since that snapshot.
Snapshot isolation (SI) has been adopted by several major database management systems, such as SQL Anywhere, InterBase, Firebird, Oracle, PostgreSQL and Microsoft SQL Server. The main reason for its adoption is that it allows better performance than serializability, yet still avoids the kind of concurrency anomalies that cannot easily be worked around. SI has also been to critique the ANSI SQL-92 standard's definition of isolation levels, as it exhibits none of the "anomalies" that the SQL standard prohibited, yet is not serializable (the anomaly-free isolation level defined by ANSI).
Tuesday, April 08, 2008
In computing, an integrated development environment (IDE) is a software application that provides comprehensive facilities to computer programmers for software development. An IDE normally consists of a source code editor, a compiler and/or interpreter, build automation tools, and (usually) a debugger. Sometimes a version control system and various tools are integrated to simplify the construction of a GUI. Many modern IDEs also have a class browser, an object inspector, and a class hierarchy diagram, for use with object oriented software development.
Friday, April 04, 2008
Database security is the system, processes, and procedures that protect a database from unintended activity. Unintended activity can be categorized as authenticated misuse, malicious attacks or inadvertent mistakes made by authorized individuals or processes. Database security is also a specialty within the broader discipline of computer security.
Traditionally databases have been protected from external connections by firewalls or routers on the network perimeter with the database environment existing on the internal network opposed to being located within a demilitarized zone. Additional network security devices that detect and alert on malicious database protocol traffic include network intrusion detection systems along with host-based intrusion detection systems.
Tuesday, March 25, 2008
A reverse proxy or surrogate is a proxy server that is installed within the neighborhood of one or more servers. Typically, reverse proxies are used in front of Web servers. All connections coming from the Internet addressed to one of the Web servers are routed through the proxy server, which may either deal with the request itself or pass the request wholly or partially to the main web servers.
A reverse proxy dispatches in-bound network traffic to a set of servers, presenting a single interface to the caller. For example, a reverse proxy could be used for load balancing a cluster of web servers. In contrast, a forward proxy acts as a proxy for out-bound traffic. For example, an ISP may use a proxy to forward HTTP traffic from its clients to external web servers on the internet; it may also cache the results to improve performance.
Tuesday, March 18, 2008
MySQL (pronounced /maɪˌɛskjuːˈɛl/ "my S-Q-L") is a multithreaded, multi-user SQL database management system (DBMS) which has more than 11 million installations. The basic program runs as a server providing multi-user access to a number of databases.
Originally financed in a similar fashion to the JBoss model, MySQL was owned and sponsored by a single for-profit firm, the Swedish company MySQL AB, now a subsidiary of Sun Microsystems, which holds the copyright to most of the codebase. The project's source code is available under terms of the GNU General Public License, as well as under a variety of proprietary agreements.
