Sum of the internal energy math.E and the product of the pressure math.P and volume math.V of a thermodynamic system (see thermodynamics). So, enthalpy math.H = math.E + math.Pmath.V. Its value is determined by the temperature, pressure, and composition of the system at any given time. According to the law of conservation of energy (see conservation law), the change in internal energy is equal to the heat transferred to the system minus the work done by the system. If the only work done is a change of volume at constant pressure, the enthalpy change is exactly equal to the heat transferred to the system.
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Content-control software can also be used to block Internet access entirely.
Companies that make products that selectively block Web sites do not refer to these products as censorware, and prefer terms such as "Internet filter" or "URL Filter"; in the specialized case of software specifically designed to allow parents to monitor and restrict the access of their children, "parental control software" is also used. Some products log all sites that a user accesses and rates them based on content type for reporting to an "accountability partner" of the person's choosing, and the term accountability software is used. Internet filters, parental control software, and/or accountability software may also be combined into one product .
Those critical of such software, however, use the term "censorware" freely: consider the Censorware Project, for example. The use of the term "censorware" in editorials criticizing makers of such software is widespread and covers many different varieties and applications: Xeni Jardin used the term in a 9 March 2006 editorial in the New York Times when discussing the use of American-made filtering software to suppress content in China; in the same month a high school student used the term to discuss the deployment of such software in his school district
In general, outside of editorial pages as described above, traditional newspapers do not use the term "censorware" in their reporting, preferring instead to use terms such as "content filter," "content control," or "web filtering"; the New York Times and the Wall Street Journal both appear to follow this practice. On the other hand, Web-based newspapers such as CNET use the term in both editorial and journalistic contexts, e.g., "Windows Live to Get Censorware."
Those who believe content-control software is useful may still not agree with certain ways it is used, or with mandatory general regulation of information. For example, many would disapprove of filtering viewpoints on moral or political issues, agreeing that this could become support for propaganda. Many would also find it unacceptable that an ISP, whether by law or by the ISP's own choice, should deploy such software without allowing the users to disable the filtering for their own connections. In addition, some argue that using content-control software may violate sections 13 and 17 of the Convention on the Rights of the Child. In 1998, a United States federal district court in Virginia ruled that the imposition of mandatory filtering in a public library violates the First Amendment of the U.S. Bill of Rights. Mainstream Loudon v. Board of Trustees of the Loudon County Library, 24 F. Supp. 2d 552 (E.D. Va. 1998)
Critics then argued that while content-filtering software might make government censorship less likely, it would do so only by allowing private companies to censor as they pleased. They further argued that government encouragement of content filtering, or legal requirements for content-labeling software, would be equivalent to censorship. Although at severe risk of being sued under charges such as copyright infringment, trade secret violation, or breach of license agreement , groups such as the Censorware Project began reverse-engineering the content-control software and decrypting the blacklists to determine what kind of sites the software blocked. They discovered that such tools routinely blocked unobjectionable sites while also failing to block intended targets. An example of this tendency was the filtering of all sites containing the word "breast", on the assumption that this word could only be mentioned in a sexual context. This approach had the consequence of blocking sites that discuss breast cancer, women's clothing, and even chicken recipes. Similarly, over-zealous attempts to block the word "sex" would block words such as "Essex" and "Sussex". For some reason, one filter blocked looking up the word "swallow" Content-control software has been cited as one of the reasons Beaver College decided to change its name to Arcadia University, as content-control software had been blocking access to the college Web site.
Some content-control software companies responded by claiming that their filtering criteria were backed by intensive manual checking. The companies' opponents argued, on the other hand, that performing the necessary checking would require resources greater than the companies possessed and that therefore their claims were not valid.
Many types of content-control software have been shown to block sites based on the religious and political leanings of the company owners. Examples include blocking several religious sites (including the Web site of the Vatican), many political sites, and sites about gay/lesbians. X-Stop was shown to block sites such as the Quaker web site, the National Journal of Sexual Orientation Law, the Heritage Foundation, and parts of The Ethical Spectacle. CYBERsitter blocks out sites like National Organization for Women. Nancy Willard, an academic researcher and attorney, reported on the close relationships between conservative Christian organizations and filtering software companies providing filters in U.S. public schools and libraries. See: Filtering Software: The Religious Connection From her review of publicly available documentation, she concluded that seven of the filtering software companies were blocking Web sites based on religious or other inappropriate bias.
Although most content control software is marketed to organizations and parents, it is also is advertised for home use as self-censorship to people struggling with internet addictions. People that spend obsessive time accessing pornography, gambling, chat rooms, or the internet in general may want to voluntarily remove or restrict access to content on the internet. Recently a number of accountability software products such as Covenant Eyes or X3Watch has been introduced as well. Many of the products marketed as self-censorship or accountability software are promoted at churches and through religious media.
The site Peacefire.org posted information about some pages that were blocked and it was then added to the blocklist. Solid Oak Software has vowed that Peacefire's reports about CYBERsitter "will be blocked wherever they may be."
ICRA labels come in a variety of formats. These include the World Wide Web Consortium's Resource Description Framework (RDF) as well as Platform for Internet Content Selection (PICS) labels used by Microsoft's Internet Explorer Content Advisor.
ICRA labels are an example of self-labeling. Similarly, in 2006 the Association of Sites Advocating Child Protection (ASACP) initiated the Restricted to Adults self-labeling initiative. ASACP members were concerned that various forms of legislation being proposed in the United States were going to have the effect of forcing adult companies to label their content. The RTA label, unlike ICRA labels, does not require a webmaster to fill out a questionnaire or sign up to use. Like ICRA the RTA label is free. Both labels are recognized by a wide variety of content-control software.
The Voluntary Content Rating (VCR) system was devised by Solid Oak Software for their CYBERsitter filtering software, as an alternative to the PICS system, which some critics deemed too complex. It employs HTML metadata tags embedded within web page documents to specify the type of content contained in the document. Only two levels are specified, mature and adult, making the specification extremely simple.
Many legal scholars believe that a number of legal cases, in particular Reno v. American Civil Liberties Union, established that the use of content-control software in libraries is a violation of the First Amendment. The Children's Internet Protection Act [CIPA] and the June 2003 case United States v. American Library Association found CIPA constitutional as a condition placed on the receipt of federal funding, stating that First Amendment concerns were dispelled by the law's provision that allowed adult library users to have the filtering software disabled, without having to explain the reasons for their request. The plurality decision left open a future "as-applied" Constitutional challenge, however. In November 2006, a lawsuit was filed against the North Central Regional Library District (NCRL) in Washington State for its policy of refusing to disable restrictions upon requests of adult patrons.
In March 2007, Virginia passed a law similar to CIPA that requires public libraries receiving state funds to use content-control software. Like CIPA, the law requires libraries to disable filters for an adult library user when requested to do so by the user.
NetAlert, the software made available free of charge by the Australian government, was cracked by a 16 year old student, Tom Wood, less than a week after its release in August 2007. Wood bypassed the $84 million filter in about half an hour to highlight problems with the government's approach to Internet content filtering.
The Australian Government has introduced legislation that required ISP to "restricting access to age restricted content (commercial MA15+ content and R18+ content) either hosted in Australia or provided from Australia" that will comment from 20 January 2008 There does not appear to be any requirement to filter "age restricted content" that is hosted outside of Australia, where a great majority of it is.
Many content filters have an option which allows authorized people to bypass the content filter. This is especially useful in environments where the computer is being supervised and the content filter is aggressively blocking Web sites that need to be accessed.
Gateway Based Content Control Solutions may be more difficult to bypass than desktop software solutions, since they are less easily removed or disabled by the local user.