An Introduction To Network Topology

An Introduction To Network Topology In the context of a communication network, the term topology refers to that way in which the end points, or stations, attached to the network are interconnected or it is the arrangements of systems in a computer network. It can be either physical or logical. The physical topology refers that, a way in which a network is laid out physically and it will include the devices, installation and location. Logical topology refers that how a data transfers in a network as opposed to its design. The network topology can be categorized into bus, ring, star, tree and mesh. Hybrid networks (They are the complex networks, which can be built of two or more topologies). Bus Topology A Bus topology is characterized by the use of a multi point medium. A long and single cable acts as a backbone to connect all the devices in a network. In a bus topology, all computers or stations attach through the appropriate hardware interfacing known as a tap, directly to a bus network. Full duplex operation between the station and tap allows data to transmit onto the bus and received from the bus. A transmission from any station propagates the length of the medium in both directions and can be received by all other stations. At each end of the bus is a terminator, which absorbs any signal, removing it from the bus. Nodes are connected to the bus cable by drop lines and taps. A drop line is a connection running between the device and the main cable. A tap is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core. A bus network work best with a limited number of computers. Advantages Bus topology can install very easily on a network. Cabling will be less compare to other topologies because of the main backbone cable laid efficiently in the network path. Bus topology suited for a small network. If one computer fails in the network, the other computers are not affected they will continue to work. It is also less expensi ve than star topology. Disadvantages The cable length will limited and there by limits the number of stations. If the backbone cable fails, the entire network will goes down. It is very difficult to trouble shoot. Maintenance cost is very high in a long run. Terminators are required for both the ends of the cable. Ring topology The ring topology the network consists of dedicated point to point connection and a set of repeaters in a closed loop. A signal is passed along the ring in one direction, from device to device, until it reaches its destination. It may be clock wise or anti clock wise. When a device receives a signal intend for another device, its repeater generates the bits and passes them along. As with the bus and tree, data are transmitted in frames. As a frame circulates past all the other stations, the destination station recognize its address and copies the frame into a local buffer as it goes by. The frame continues to circulate until it returns to the source station, where it is removed. These topologies are used in school campuses and some office buildings.

Transmission Electron Microscopy Coursework Example | Topics and Well Written Essays - 3000 words

Transmission Electron Microscopy - Coursework Example With the support of ray, diagrams explain how the images were obtained. Your explanation must include comments about the location and use of the objective and selected area apertures. A TEM consists of condenser lenses to focus the electron beam on the specimen, an objective lens to form diffraction in the BFP (Back focal plane) and the image in the image plane, and other lenses to magnify the image or the diffraction pattern on the screen. In order to obtain images in TEM, we either focus on the central spot (direct beam), or on the scattered electrons (diffracted beam). This is done by inserting an aperture (selected area aperture) into the BFP of the objective lens followed by selecting the appropriate beam. Bright field image (Figure 1) The given micrograph depicts a dark MgO crystal on a light and bright background. The topography on the face of the crystal is very clear. Such an image is called a bright field image and has a very high contrast. ...The parts of the crystal in Br agg orientation appear dark, and the amorphous parts of the crystal are bright. The objective diaphragm is adjusted in such a way that an aperture appears in the back focal plane of the objective lens, allowing only the direct beam to enter and blocking the diffracted beam. The objective aperture, when inserted, controls the collection angle. The placement of the SAD (selected area aperture) is critical as it should be adjusted to obtain only the direct beam in this case. Darkfield image (Figure 2) The micrograph in figure two depicts a bright MgO crystal on a dark background. Such an image is obtained by selecting only the scattered electrons using a selected area aperture, enabling them to reach the image plane. The electrons that are not in the direct beam are selected to form a dark field image. The objective aperture is moved sideways to select the un-scattered electrons. This method is of high utility in case of observing certain specific crystallographic orientations of the s pecimen. The dark field image can also be obtained through another method, called centered dark field operation. In this case, the objective aperture is not shifted and the primary/direct beam is used instead. "The beam is tilted in order to allow only the scattered/diffracted electrons to go through the objective aperture (William and Carter 2009). Selected area diffraction pattern SAED (Figure 7) The given micrograph clearly depicts the symmetry of the lattice of MgO crystal through a selected area diffraction pattern. Selected area diffraction patterns are obtained by inserting the SAD aperture into the image plane of the objective lens and aperture on the optic axis in the middle of the viewing screen (William and Carter 2009).

Social Promlem project on Internet Addiction Essay

Social Promlem project on Internet Addiction - Essay Example Moving further, we will look into various types of internet addiction. After this, we will be exploring the effect of gender difference on the internet addiction. Furthermore, the discussion would be led to the causes and the development of the internet addiction. Last, but not the least, we will be looking over various treatment options for the internet addiction. So we can say, in general terms, that addiction is the process of getting habitual to the use of something. In the same connection, internet addiction is, in layman terms, the habitual use of internet or being compulsively occupied with the use of internet. "Technical addictions... non-chemical (behavioral) addictions which involve human-machine interaction. They can either be passive (e.g. television) or active, (e.g. computer games) and usually contain inducing and reinforcing features which may contribute to the promotion of addictive tendencies". (Griffths, 2000) Various experts have also called it cyber addiction. "Cyberspace Addiction: an addiction to virtual realms of experience created through computer engineering... Some cyberspace addictions are game and competition oriented, some fulfill more social needs, some simply may be an extension of workaholicism". (Suler, 1999) All in all, internet addiction, with whatever term it may be referred, is the excessive use of internet to the extent that a person become compulsively engaged in using the internet. Types of Internet Addiction The internet addiction can be classified into a number of typologies. However, the most commonly used typology among the scholarly circles is that based on the usage. On this basis, the internet addiction can be divided into following types: Addiction for Internet Sex Addiction for Games over Internet Addiction for Making Money over Internet Addiction for Chat Addiction for Web Surfing This typology has been adapted from the works of Young (et al. 1999) and Davis (2001). Addiction for Internet Sex According to some estimates, the total worth of the online sex industry is somewhere between 1 and 5 billion US Dollars. Moreover, the sex industry over internet has become one of the major contributors among the total revenue generated through the paid websites (McDonald, 2001). There are also some estimates that the highest search queries on various search engines, such as Google and Yahoo etc, are related to pornography, especially among teens. The internet is heavily with the sex related material. That includes, sex related text (stories), images, video, audio stories and entire DVD format full length