Application-level gateway
In the context of computer networking, an application-level gateway [1] (also known as ALG or application layer gateway) consists of a security component that augments a firewall or NAT employed in a computer network. It allows customized NAT traversal filters to be plugged into the gateway to support address and port translation for certain application layer "control/data" protocols such as FTP, BitTorrent, SIP, RTSP, file transfer in IM applications etc. In order for these protocols to work through NAT or a firewall, either the application has to know about an address/port number combination that allows incoming packets, or the NAT has to monitor the control traffic and open up port mappings (firewall pinhole) dynamically as required. Legitimate application data can thus be passed through the security checks of the firewall or NAT that would have otherwise restricted the traffic for not meeting its limited filter criteria.
Monday, March 24, 2008
Monday, March 17, 2008
Waterfall model
The waterfall model is a sequential software development model (a process for the creation of software) in which development is seen as flowing steadily downwards (like a waterfall) through the phases of requirements analysis, design, implementation, testing (validation), integration, and maintenance. The origin of the term "waterfall" is often cited to be an article published in 1970 by Winston W. Royce (1929–1995),[1] although Royce did not use the term "waterfall" in this article. Ironically, Royce was actually presenting this model as an example of a flawed, non-working model (Royce 1970).
The waterfall model is a sequential software development model (a process for the creation of software) in which development is seen as flowing steadily downwards (like a waterfall) through the phases of requirements analysis, design, implementation, testing (validation), integration, and maintenance. The origin of the term "waterfall" is often cited to be an article published in 1970 by Winston W. Royce (1929–1995),[1] although Royce did not use the term "waterfall" in this article. Ironically, Royce was actually presenting this model as an example of a flawed, non-working model (Royce 1970).
Sunday, March 09, 2008
Field emission display (FED)
A field emission display (FED) is a type of flat panel display using field emitting cathodes to bombard phosphor coatings as the light emissive medium.
Field emission displays are very similar to cathode ray tubes, however they are only a few millimeters thick. Instead of a single electron gun, a field emission display (FED) uses a large array of fine metal tips or carbon nanotubes (which are the most efficient electron emitters known), with many positioned behind each phosphor dot, to emit electrons through a process known as field emission. Because of emitter redundancy, FEDs do not display dead pixels like LCDs even if 20% of the emitters fail. Sony is researching FED because it is the flat-panel technology that comes closest to matching the picture of a CRT.
A field emission display (FED) is a type of flat panel display using field emitting cathodes to bombard phosphor coatings as the light emissive medium.
Field emission displays are very similar to cathode ray tubes, however they are only a few millimeters thick. Instead of a single electron gun, a field emission display (FED) uses a large array of fine metal tips or carbon nanotubes (which are the most efficient electron emitters known), with many positioned behind each phosphor dot, to emit electrons through a process known as field emission. Because of emitter redundancy, FEDs do not display dead pixels like LCDs even if 20% of the emitters fail. Sony is researching FED because it is the flat-panel technology that comes closest to matching the picture of a CRT.
Tuesday, March 04, 2008
Methods for solids
Computational chemical methods can be applied to solid state physics problems. The electronic structure of a crystal is in general described by a band structure, which defines the energies of electron orbitals for each point in the Brillouin zone. Ab initio and semi-empirical calculations yield orbital energies, therefore they can be applied to band structure calculations. Since it is time-consuming to calculate the energy for a molecule, it is even more time-consuming to calculate them for the entire list of points in the Brillouin zone.
Computational chemical methods can be applied to solid state physics problems. The electronic structure of a crystal is in general described by a band structure, which defines the energies of electron orbitals for each point in the Brillouin zone. Ab initio and semi-empirical calculations yield orbital energies, therefore they can be applied to band structure calculations. Since it is time-consuming to calculate the energy for a molecule, it is even more time-consuming to calculate them for the entire list of points in the Brillouin zone.
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