Compare and Contrast Vertebrate and Invertebrate Vision Essays

Compare and Contrast Vertebrate and Invertebrate Vision Essays Compare and Contrast Vertebrate and Invertebrate Vision Paper Compare and Contrast Vertebrate and Invertebrate Vision Paper Although vertebrates and invertebrates originally evolved from a common ancestral root, both have developed very different physical utilities for vision. Both are fairly effective and have taken many millions of years to evolve. They contain many common underlying mechanisms but differ in the features used to provide them. The definition of an eye is an organ of visual perception that includes parts specialized for optical processing of light as well as well as photoreceptive neurons (Alberts). The main feature of an eye therefore, in all organisms that possess one, is the collection of photoreceptors used in converting light energy into action potentials (electrical energy). When comparing vertebrate and invertebrate vision, the two best-studied cases are the compound eye exemplified by arthropods and the simple eye used in vertebrates. The main difference between the compound and simple eye is that the compound eye uses a spatial array of lenses so that each image in a local region of visual space falls onto one or a few photoreceptors. The simple eye, however, uses a single lens to image the world onto an array of photoreceptors. Compound eyes produce mosaic images. The compound eye is made up of many optical units called ommatidiums, each of which is aimed at a different part of the visual field. Each ommatidium samples a different part of the visual field through a separate lens. In a simple eye, each receptor cell samples part of the field through a lens shared by all receptor cells. In compound eyes, each ommatidium samples an angular cone-shaped portion of the environment, taking in about 2-3i of the visual field. In contrast, each receptor of a simple eye may sample as little as 0. 2i of the visual field. In addition, the simple eye, inverts the image that falls on the retina. Since the receptive field of each ommatidium is relatively large, compound eyes have lower visual acuity than simple eyes. The mosaic image formed by a compound eye is also coarser than that of a simple eye. The simple eye in vertebrates focuses incident light in two stages. In the initial stage, incident light rays are refracted as they pass through the clear outer surface of the eye, called the cornea. They are further refracted as they pass through a second structure, the lens, and finally form an inverted image on the rear internal surface of the eye, the retina. Objects at different distance can be focussed in higher vertebrates by changing the curvature and thickness of the lens, which affects its focal length, the distance at which an image passed through the lens comes into focus. Diffraction is a property of all light and because of this, the angular resolution (resolving power) of any eye is limited by the diameter of its lens. The larger the lens diameter, the higher spatial resolution. The biggest problem for compound eyes is that the resolution is limited because the facets of the individual lens are so small. A compound eye of a given size will have a much lower resolving power than a simple eye of the same size. Optical superposition compound eyes are one way of increasing the effective lens diameter. This structure works by using several separate elements to image incident rays onto a single point, such as a single photoreceptor. This method is used in insects such as fireflies. Another way, is to use neural superposition. Simple eyes on the other hand, use a single lens, and have evolved entirely separately in the cephalopods and vertebrates. The octopus is a good example because the optical design of its eyes is remarkably similar to the vertebrate eye. The one major difference, however is that in octopus eyes, as in all fish eyes, the lens is much more powerful because it has to compensate for the loss in refractive power from the cornea, due to being underwater. Simple eyes have a much larger lens diameter which means that the spatial resolution achievable is much higher than is ever possible with a compound eye. Experiments by Kirschfeld have suggested that in order to obtain the same spatial resolution as a human eye, a compound eye would need to be about 1m across. The eye is a complex structure which has caused many arguments between evolutionary biologists and theologists. Theologists believe that the eye is so perfectly designed to harvest light, and that no intermediary design would be effective, that it must have been created by a divine designer. Biologists believe that it was created step-by-step through natural selection, and that any one step is always an improvement on the last, and thus the eye did not have to be this complex to be of benefit. This argument can be backed up by the evidence of optical diseases in which humans are handicapped in their sight, yet to them, the vision they have is better than none at all, as was a primitive form of an eye. Myopia (short-sightedness) and hypermetropia (long-sightedness) occur when the optical image of a point at infinity (i. e. he far point) falls respectively in front of or behind the retina. These errors commonly occur when the eyeball is too long, or too short, and is easily corrected with a concave or convex lens. These diseases are commonly found amongst the elderly who no longer have such deformable lens and so have difficulty varying the curvature of the lens, and thus focussing on objects at different distances effectively. This is an accommodation problem. Accommodation (discovered by Helmholz) is brought about by the ciliary body that acts on the zonular fibres that support the lens. It contains circumferential (circular) muscle fibres that allow it to act as a sphincter. The lens can be dilated by relaxing the circumferential fibres, and is said to be unaccommodated. The radial fibres of the ciliary body also act by pulling outwards on the zonular fibres that support the lens, thereby thinning it. The lens is accommodated when the circumferential fibres contract, and the lens is forced to shrink. The tension in the zonular fibres is reduced, and the lens is allowed to relax into a thicker, more curved shape, with greater refractive power. A related neuronal mechanism produces binocular convergence, in which the left and right eyes are positioned by the ocular muscles so that the images received by the two eyes fall on analogous parts of the two retinas, regardless of the distance between the object and the eyes. When an object is close, each of the two eyes must rotate towards the middle of the nose; when an object is far away, the two eyes rotate outward from the midline. Photoreceptors transduce photons of electromagnetic radiation from the visible light spectrum, into electrical signals that can be interpreted by the nervous system. The energy of the electromagnetic radiation varies inversely with its wavelength, and we perceive this variation in energy as variation in colour. The outermost layer of the vertebrate retina includes two classes of photoreceptor in vertebrates: rods and cones. There are about 100 million rods in the eye and 5 million cones. A small central area called the fovea, is densely packed with cones, but in the periphery, rods outnumber cones by 20:1. Cones function best in bright light and provide high resolution, whereas rods function best in dim light but provide much less resolution. In humans, cones mediate colour vision, and rods mediate achromatic vision. These different properties are used to expand the visual capabilities of animals living in certain conditions. For example, animals that live in flat, open environments such as rabbits, usually have horizontal regions within the retina that contain a high density of cones. This concentration of cones is called the visual streak. This region corresponds to the horizon in the visual world and is thought to confer maximal resolution in this part of the scene, allowing the animal to interpret shapes on the horizon with great precision. A receptor current exists for all sensory receptors which are usually modulated by the stimulus. In the case of vertebrate photoreceptors, the light stimulus actually reduces the circulating current, by causing the closure of ion channels. Although both invertebrates and vertebrates have eyes containing photoreceptors, they differ in their structure. Vertebrate receptor cells contain a segment with an internal structure similar to that of a cilium. This cilium connects the outer segment, which contains the photoreceptive membranes to the inner segment, which includes the nucleus and mitochondria. The photoreceptors of many invertebrates lack the ciliary structure that connects the inner and outer segments of vertebrate rods and cones and the lamellae and or stacks of disks containing visual pigment. Instead, the visual pigment is located in the microvilli formed by the plasma membrane, and these pigment-containing microvilli are organised into rhabdomeres. Visual pigments consist of 2 major components: a protein (opsin) and a light-absorbing molecule (either retinal or 3-dehydroretinal). Opsins are protein visual pigment molecules consisting of 7 transmembrane ? -helix domains. Opsins are coupled to photopigment molecules that are structurally altered by the absorption of photons, and in turn modify the opsin protein. The retinal molecule assumes two sterically distinct states in the retina. In the absence of light, the opsin and retinal are linked covalently and retinal is in an 11-cis formation. The covalent bond allows this light-absorbing molecule to act as a powerful antagonist. On capturing a photon, the retinal isomerises into the all-trans configuration, initiating a series of changes in the visual pigment, as the molecule is rendered enzymatically active. When light hits the photopigment, an intermediate metharhodopsin II forms that activates the G-protein transducin. Transducin activity closes Na+ channels and the receptor cell hyperpolarizes. Activated rhodopsin is hydrolysed spontaneously to retinal and rhodopsin which is hydrolysed spontaneously to retinal and opsin which are both used repeatedly. Studies made on the horseshoe crab, Limulus polyphemus have revealed a lot about vision. The crab has paired lateral compound eyes as well as five simple eyes: medial and lateral pairs on the dorsal surface and a single unpaired simple eye on the ventral surface. The compound eyes are typical compound eyes whereas the simple eyes are similar in structure to the simplest eye known, which consists of a shallow open pit lined with photoreceptor cells that are backed by screening pigment. Each ommatidium of a compound eye contains several photoreceptor cells. The photoreceptor cells of the Limulus compound eye are located at the base of each ommatidium. Each ommatidium lies beneath a hexagonal section of an outer transparent layer, the corneal lens. Visual transduction takes place in 12 retinular, or photoreceptor, cells. Each retinular cell has a rhabdomere, a part of the cell in which the plasma membrane is thrown into densely packed microvilli, making this the part of the cell that captures light energy. The microvilli greatly increase the surface area of the plasma membrane, which increases the probability that incident light will be captured by the rhodopsin molecules embedded in the membrane. Together, the 12 rhabdomeres of the retinular cells make up a rhabdome, which surrounds the dendrite of an afferent neuron, the eccentric cell. Depolarisations of the plasma membrane can be recorded in the retinular cells when the eye is exposed to very dim light. These quantum bumps increase in frequency as the light intensity increases (i. e. as more photons impinge on the receptors). The bumps are electrical signals generated as a result of the absorption of individual quanta of light. How can capture of a single photon lead to rapid release of so much energy? In this case, through a cascade of chemical reactions inside the cell that includes G-protein activation. Activation of the G-protein cascade occurs by diffusional contact between activated rhodopsin and molecules of G-protein, which are activated sequentially, as explained above; the activated g-protein in turn activates an effector enzyme, the PDE (phosphodiesterase); this is a 1:1 step, i. e. it has no amplification. A second stage of amplification occurs because the activated PDE is an enzyme which catalyses the destruction of cGMP. The net effect is to open ion channels, allowing cations to enter the cell. In Limulus, the receptor current through the light activated channels is carried by Na+, K+ and some Ca2+. This current causes a depolarising receptor potential. When the light goes off, the channels close again, and the membrane repolarises. The sensitivity of individual photoreceptors drops with exposure to light. This light adaptation is thought to be mediated by Ca+ ions, which enter the cells when light causes ion channels to open and which by some mechanism then reduce the current through light-activated channels. Although the Limulus eye is simple compared to that of invertebrates, the visual system is capable of generating electrical activity that parallels some of the more sophisticated features of human visual perception. The crab does however lack the degree of colour perception seen by the human eye, because it lacks the short and long wave colour pigments in its cones. It is interesting to see how two totally different mechanisms of visual perception can be so different yet interrelated in many ways, and that they have involved independently to perform the same function.

Investigation of Current Performance in Inverleith Hotel (B&B) Edinbur Assignment

Investigation of Current Performance in Inverleith Hotel (B&B) Edinburg - Assignment Example Additionally, a SWOT analysis of the hotel has been conducted with the aim of understanding strengths, weaknesses, opportunities and threats of Inverleith Hotel (B&B) located in Edinburgh, which is a B&B hotel. A comparison is also made between the hotel with other similar size B&B hotels in the same geographical area. Alternatively, it also intends to explain the methods through which the current performance of the hotel can be maintained properly and the possible solutions for the expansion of the business. In order to determine strengths, weaknesses, opportunities and threats of Inverleith Hotel (B&B), a SWOT analysis has been conducted. In this respect, the strengths, as well as weaknesses of the hotel, can be determined. The possible opportunities related to the success and development of the hotel can also be ascertained. After identifying the weaknesses and threats, the hotel can reduce the weakness by applying new strategies to improve the performance of the hotel (Practical Entrepreneurship, n.d.). The hotel is one of the leading fast food hotels in England. The hotel focuses on the preferences of the customers, which is one of the important strength of the hotel. This strength helps the hotel to attract the more customers to increase the sale as well as increase the profit of the hotel. It also helps to improve the performance of the employees so that the objectives of the hotel can be accomplished. It has multiple numbers of customers in the market. The financial growth of the hotel has increased to a substantial extent. The geographical area of the hotel is good for marketing or doing business. The facilities provided by the hotel are based on quality standards and in accordance with the needs of the customers. The rooms of the hotel are equipped with modern equipment like telephone and broadband access and with self-catering accommodation (Practical Entrepreneurship, n.d.).

Task Force Smith (Korean War) Research Paper Example | Topics and Well Written Essays - 2500 words

Task Force Smith (Korean War) - Research Paper Example Introduction The term, â€Å"Task Force Smith† derives the ill-fated battle between the United States of America (USA) and the Republic of Korea (ROK) where U.S.A lost shamefully to the opponents. The cause of the loss resulted from machinery and artillery incompetence. The Americans, under the command of Colonel Charles B. Smith, engaged in the battlefield with lesser powerful weapons as compared to the North Koreans (Murray, 2005). The troop set foot on the Korean land at a time that the enemy was advancing. The U.S.A had assumed a tremendous win following that of the Second World War. They did not train prior to the battle, used poor equipment, and approached the battle with a troop of 514 men (United States, 2007). The following outlines the deeper script of the turn of events, the artillery used to attack the enemy, the result of the war and the eventual failure of the American troops under the command of Lieutenant Colonel Charles B. Smith. The cause of the war In the ye ar 1950, North Korea advanced towards South Korea, three years after the Second World War, thus, provoking a battle over territorial rights. The North was fully prepared to war unlike their neighbors with whom they caught unawares. South Korea, being weak in military skills and weaponry, seek help from U.S.A thinking that it would help defeat the enemy, but this posed more than enough challenges to U.S. America lacked enough and most recent ammunition thus, they declined to attend the war (McMurran, 2008). The South Koreans further pleaded for help and the U.S.A offered two-week training to the Korean army. After the two weeks training, America applauded South Korean Military and commented on their degree of integrity and the skill, they now possessed to retaliate against the enemy. The South Koreans, overwhelmed by the praises, proceeded to the battlefield with a lion heart, as they perceived a win over an enemy they did not analyze (United States, 2007). South Koreans depended ful ly on guns, while their enemy had the best weaponry from the Soviets. Approximately, the north possessed over 34 tanks each with 88mm caliber. However, this did not distract the Southerners as they pursued their enemy to the battlefront. The turn of events was extremely sad as they lost their lives to the mortars and shelling of the North Korean tanks and troops. South Koreans fought relentlessly to win their bid over the sophisticated enemy (McMurran, 2008). All their efforts bore no fruits, and many lost their lives to the battle thus; they slowly retreated. America got the news at the same time that the southerners’ were retreating from the battlefield. America deployed 514 men to combat the vulnerable enemy, unknown to them that the enemy rest prepared (Edwards, 2010). The U.S.A troop and its government overlooked North Korea’s potentials in the battlefield and underestimated them altogether. North Korea had already forecasted chances that the Second World War winn er would intervene into the battle were similarly high, and this led to the massive preparation in training, equipment, and competent troops. U.S.A assumed that, on stepping grounds, northerner’s would retrieve from the battle and eventually surrender. Therefore, it did not hit to them that, the northerners would dare stand them despite their number. On the contrary, North Korea remained adequately prepared to conquer the enemy, thus instead of retreating, they proceeded further into the battlefront to counter the advancing U.S.A troop

Research funding of medical product development Essay Example for Free

Research funding of medical product development Essay Alzheimer’s disease is one of the most common ailments in adults especially the old. Over 26.6 million people around the world are affected by the disease with an increase expected in the coming years. So far, there has been no established cure for the disease whose results are pain and suffering in the patients and death. With these facts, research that can lead to success in tackling this global calamity would be instrumental and welcome. This makes it critical and worth for any form of funding to be provided in any research towards elimination of the same. The document evaluates the various forms of funding available which would help in the research to develop a novel compound critical in controlling and even curing the disease. Discussion National governments are one of the biggest sources of funding for clinical research. Various governments set aside some money in their Health sector budget of which a big portion includes money for research. The government funding programs operate locally or internationally (Murray Johnston, 2010). An example in national government funding is the NIH (National Institute of Health) which through its various sections such as the National Human Genome Research Institute provides funding for research projects in America (Kulakowski, 2006). For the case of research in Alzheimer’s disease, national funding is through the National Institute on Aging. Government funding is beneficial in that they are not discriminative compared to funding from other sources such as organizations. However, one disadvantage is that the funds may take long thus jeopardizing the research (Kaitin, 2010). Associated closely with national governments and also a source of funding are government agencies. Agencies operate both nationally and internationally (Shaw, 2005). An example of such an agency is the Department of Energy in America. The agencies provide the funds to different sub-divisions of research areas, for example, the Human Genome Project section which may assist in developing the compound identified (Boss Eckert, 2006). With their international operations, the benefit is that the agencies will fund any project that fulfills its requirements. One disadvantage however is that agencies are prone to manipulation and thus may be biased in funding projects due to political differences (Smith, 2006). Another source of funding for scientific research projects are foundations. These entities have a wide range of research requirements and interests (Hulley, 2007). Some of the foundations will be specific in the areas they want to fund such as the American Cancer Society that focuses on Cancer. Others are open for any research in any area such as the Howard Hughes Medical Institute which provides funding for various areas, for example, Alzheimer’s disease (Reinhart National Research Council, 2006). Brightfocus Foundation and Alzheimer’s Research Foundation are some of the foundations that focus on funding Alzheimer based research (Financing roundup, 2008). The benefit in using foundations is that they span a wide range of research areas thus a big chance of being funded (Clinical research in Finland in 2002 and 2007, 2013). There is a disadvantage in that funding from foundations is subject to misappropriation through vices such as corruption affects the operations (Ca mbron, 2008). Many individuals have been known to offer private funding for research projects all over the world. Wealthy individuals are now funding scientific research institutions or individual based ones (Page, 2012). Armand Hammer, former chairman of Occidental Petroleum Corporation is an example. For his case, he provided funding for cancer related projects (Lee, 2010). Another example is Ronald Perelman and Lilly Tartikoff who funded the Revlon/ UCLA women’s Cancer Research Program under the leadership of Salmon (Bazell Bernstein, 1998). One advantage of funding from individuals is that there are no rigorous processes involved in obtaining the funds like is the case with government agencies and foundations. A disadvantage in using the same is that individual funding may be withdrawn when differences arise thus stalling the research (Kullmann, 2006). References Bazell, R., Bernstein, A. (1998). Her-2: The making of herceptin, a revolutionary treatment for breast cancer. New York: Random House. Boss, J. M., Eckert, S. H. (2006). Academic scientists at work. New York, NY: Springer. Cambron, J. (2008). Grant funding for elderly health services (6th ed.). Manasquan, NJ: Health Resources Publishing. Clinical research in Finland in 2002 and 2007: Quantity and type. (2013). BioMed Central.Financings roundup.(Harvard University Office of Technology Development is funding for research projects in biomedical and life sciences )(Report). (2008, February 11). Medical Device Week.Hulley, S. (2007). Designing clinical research (3rd ed.). Philadelphia, PA: Lippincott Williams Wilkins. Kaitin, K. (2010). (video) Research funding of medical product development.Kulakowski, E. (2006). Research administration and management. Sudbury, Mass.: Jones and Bartlett. Kullmann, P. (2012). The Inventors Guide for Medical Technology From Your Napkin to the Market. Minneapolis: Hillcrest Media Group. Lee, J. (2010). Biomedical engineering entrepreneurship. Singapore: World Scientific. Murray, T. H., Johnston, J. (2010). Trust and integrity in biomedical research: The case of financial conflicts of interest. Baltimore: Johns Hopkins University Press. Page, P. (2012). An introduction to clinical research. Oxford: Oxford University Press. Reinhart, G. R., National Research Council (U.S.). (2006). Enhancing philanthropys support of biomedical scientists: Proceedings of a workshop on evaluation. Washington, DC: National Academies Press. Shaw, G. (2005, October). Tapping Alternative Sources: Funding Beyond the NIH. G P, 5(8)12-18. Smith, C. (2006). The process of new drug discovery and development (2nd ed.). New York: Informa Healthcare. Source document

The Impact of Videoconferencing in Organizations Essay -- Videoconfere

The Impact of Videoconferencing in Organizations This report analyses the various influences of videoconferencing, both positive and negative, and evaluates its usefulness in organisations. One of the major points of discussion is how face-to-face meetings, whether virtual or physical, have been affected by the embracing of this new technology by various organisations and groups. Due to the radical nature in which traditional meetings and appointments have been challenged by videoconferencing, many issues have arisen regarding its application, like whether video-conferencing actually improves communication? Another important discussion involves the cost-saving benefits to organisations, primarily through reducing travel, and how this affects organisations strategically as well as other industries (i.e. hotels, airlines). Since many organisations now compete and communicate internationally, this potential elimination of travel for businessmen and women has far-reaching consequences. This essay seeks to explore these and other issues using three major themes: ICTs have unexpected and paradoxical effects, costs and benefits of ICTs are unevenly distributed throughout organizations and society, and ICTs and socio-technical context are co-produced. INTRODUCTION AND SUMMARY Videoconferencing is an emerging technology which enables people from any location, with the appropriate set of equipment, to communicate with each other in a virtual ‘face-to-face’ manner. The impact of videoconferencing on organizations has been extensive, with the effects of this technology growing as it becomes more user-friendly and the cost of equipment decreases. As a promising technological advance, videoconferencing has already had recent impacts upon some organisations. From a positive perspective videoconferencing has permitted things like decreases in costs, greater flexibility, and heightened strategic opportunities. Nevertheless, caution must still be applied to videoconferencing, like any new device, with concern now emerging regarding the negative consequences of such technology. These extend too many areas for example interaction, psychological outcomes, and team dynamics. POSITIVE OUTCOMES A primary impact of videoconferencing is that it allows more people to conduct work from home. This has many implications such as reducing the levels of trav... ...ay, Sarah. ‘The world of e-mail and videoconferencing has its advantages and disadvantages’. Financial Times. 5/6/02, p.3 17.  Ã‚  Ã‚  Ã‚  Ã‚  Narraway, Gwyn. ‘Take back the power’. Chartered Accountants Journal of New Zealand, Volume 82 No5: 58, 2003 18.  Ã‚  Ã‚  Ã‚  Ã‚  Neuman, Scott. ‘Executives on a leash’. Far Eastern Economic Review, Volume 166 No.27: 35, 2003 19.  Ã‚  Ã‚  Ã‚  Ã‚  Powell, Dave. ‘Videoconferencing: A wise strategy’. Computer World, Volume 32 No28: 63-68, 1999 20.  Ã‚  Ã‚  Ã‚  Ã‚  Rosen, Sheir. ‘Keeping technology in its place’. Communication World, Volume 11 No6: 56, 1994 21.  Ã‚  Ã‚  Ã‚  Ã‚  Schneider, Ivan. ‘Videoconferencing a hit in China’. Bank Systems and Technology, Volume 40 No2: 12, 2003 22.  Ã‚  Ã‚  Ã‚  Ã‚  Vine, Phillipa. ‘A meeting of minds’. The British Journal of Administrative Management, Volume 7 No4 12-13, 1999 23.  Ã‚  Ã‚  Ã‚  Ã‚  Whittaker, Steve. ‘Rethinking video as a technology for interpersonal communications: theory and design implications’. International Journal of Human-Computer Studies, Volume 42 No5: 501-529, 1995 24.  Ã‚  Ã‚  Ã‚  Ã‚  Wong, Edward. ‘Even After Sars Airlines Suffer On Asian Routes’. New York Times. 12/8/03. p.4 25.  Ã‚  Ã‚  Ã‚  Ã‚  Zielinski, Dave. ‘Face Value’. Presentations, Volume 14 No6: 58-70, 2000

Advantages and Disadvantages of Normal Lan vs. Wireless Lan

Advantages and disadvantages of normal LAN vs. wireless LAN. Computer networks for the home and small business can be built using either wired or wireless technology. Wired Ethernet has been the traditional choice in homes, but Wi-Fi wireless technologies are gaining ground fast. Both wired and wireless can claim advantages over the other; both represent viable options for home and other local area networks (LANs). Below we compare wired and wireless networking in five key areas: †¢ease of installation †¢total cost †¢reliability †¢performance †¢security About Wired LANs Wired LANs use Ethernet cables and network adapters. Although two computers can be directly wired to each other using an Ethernet crossover cable, wired LANs generally also require central devices like hubs, switches, or routers to accommodate more computers. For dial-up connections to the Internet, the computer hosting the modem must run Internet Connection Sharing or similar software to share the connection with all other computers on the LAN. Broadband routers allow easier sharing of cable modem or DSL Internet connections, plus they often include built-in firewall support. Installation Ethernet cables must be run from each computer to another computer or to the central device. It can be time-consuming and difficult to run cables under the floor or through walls, especially when computers sit in different rooms. Some newer homes are pre-wired with CAT5 cable, greatly simplifying the cabling process and minimizing unsightly cable runs. The correct cabling configuration for a wired LAN varies depending on the mix of devices, the type of Internet connection, and whether internal or external modems are used. However, none of these options pose any more difficulty than, for example, wiring a home theater system. After hardware installation, the remaining steps in configuring either wired or wireless LANs do not differ much. Both rely on standard Internet Protocol and network operating system configuration options. Laptops and other portable devices often enjoy greater mobility in wireless home network installations (at least for as long as their batteries allow). Cost Ethernet cables, hubs and switches are very inexpensive. Some connection sharing software packages, like ICS, are free; some cost a nominal fee. Broadband routers cost more, but these are optional components of a wired LAN, and their higher cost is offset by the benefit of easier installation and built-in security features. Reliability Ethernet cables, hubs and switches are extremely reliable, mainly because manufacturers have been continually improving Ethernet technology over several decades. Loose cables likely remain the single most common and annoying source of failure in a wired network. When installing a wired LAN or moving any of the components later, be sure to carefully check the cable connections. Broadband routers have also suffered from some reliability problems in the past. Unlike other Ethernet gear, these products are relatively new, multi-function devices. Broadband routers have matured over the past several years and their reliability has improved greatly. Performance Wired LANs offer superior performance. Traditional Ethernet connections offer only 10Mbps bandwidth, but 100 Mbps Fast Ethernet technology costs little more and is readily available. Although 100 Mbps represents a theoretical maximum performance never really achieved in practice, Fast Ethernet should be sufficient for home file sharing, gaming, and high-speed Internet access for many years into the future. Wired LANs utilizing hubs can suffer performance slowdown if computers heavily utilize the network simultaneously. Use Ethernet switches instead of hubs to avoid this problem; a switch costs little more than a hub. Security For any wired LAN connected to the Internet, firewalls are the primary security consideration. Wired Ethernet hubs and switches do not support firewalls. However, firewall software products like ZoneAlarm can be installed on the computers themselves. Broadband routers offer equivalent firewall capability built into the device, configurable through its own software. About Wireless LANs Popular WLAN technologies all follow one of the three main Wi-Fi communication standards. The benefits of wireless networking depend on the standard employed: †¢802. 11b was the first standard to be widely used in WLANs. †¢The 802. 11a standard is faster but more expensive than 802. 11b; 802. 11a is more commonly found in business networks. †¢The newest standard, 802. 11g, attempts to combine the best of both 802. 1a and 802. 11b, though it too is more a more expensive home networking option. Installation Wi-Fi networks can be configured in two different ways: †¢Ã¢â‚¬ Ad hoc† mode allows wireless devices to communicate in peer-to-peer mode with each other. †¢Ã¢â‚¬ Infrastructure† mode allows wireless devices to comm unicate with a central node that in turn can communicate with wired nodes on that LAN. Most LANs require infrastructure mode to access the Internet, a local printer, or other wired services, whereas ad hoc mode supports only basic file sharing between wireless devices. Both Wi-Fi modes require wireless network adapters, sometimes called WLAN cards. Infrastructure mode WLANs additionally require a central device called the access point. The access point must be installed in a central location where wireless radio signals can reach it with minimal interference. Although Wi-Fi signals typically reach 100 feet (30 m) or more, obstructions like walls can greatly reduce their range. Cost Wireless gear costs somewhat more than the equivalent wired Ethernet products. At full retail prices, wireless adapters and access points may cost three or four times as much as Ethernet cable adapters and hubs/switches, respectively. 802. 1b products have dropped in price considerably with the release of 802. 11g, and obviously, bargain sales can be found if shoppers are persistent. Reliability Wireless LANs suffer a few more reliability problems than wired LANs, though perhaps not enough to be a significant concern. 802. 11b and 802. 11g wireless signals are subject to interference from other home applicances including microwave ovens, cordless tel ephones, and garage door openers. With careful installation, the likelihood of interference can be minimized. Wireless networking products, particularly those that implement 802. 11g, are comparatively new. As with any new technology, expect it will take time for these products to mature. Performance Wireless LANs using 802. 11b support a maximum theoretical bandwidth of 11 Mbps, roughly the same as that of old, traditional Ethernet. 802. 11a and 802. 11g WLANs support 54 Mbps, that is approximately one-half the bandwidth of Fast Ethernet. Furthermore, Wi-Fi performance is distance sensitive, meaning that maximum performance will degrade on computers farther away from the access point or other communication endpoint. As more wireless devices utilize the WLAN more heavily, performance degrades even further. Overall, the performance of 802. 11a and 802. 11g is sufficient for home Internet connection sharing and file sharing, but generally not sufficient for home LAN gaming. The greater mobility of wireless LANs helps offset the performance disadvantage. Mobile computers do not need to be tied to an Ethernet cable and can roam freely within the WLAN range. However, many home computers are larger desktop models, and even mobile computers must sometimes be tied to an electrical cord and outlet for power. This undermines the mobility advantage of WLANs in many homes. Security In theory, wireless LANs are less secure than wired LANs, because wireless communication signals travel through the air and can easily be intercepted. To prove their point, some engineers have promoted the practice of wardriving, that involves traveling through a residential area with Wi-Fi equipment scanning the airwaves for unprotected WLANs. On balance, though, the weaknesses of wireless security are more theoretical than practical. WLANs protect their data through the Wired Equivalent Privacy (WEP) encryption standard, that makes wireless communications reasonably as safe as wired ones in homes. No computer network is completely secure and homeowners should research this topic to ensure they are aware of and comfortable with the risks. Important security considerations for homeowners tend to not be related to whether the network is wired or wireless but rather ensuring: †¢the home's Internet firewall is properly configured †¢the family is familiar with the danger of Internet â€Å"spoof emails† and how to recognize them †¢the family is familiar with the concept of â€Å"spyware† and how to avoid it †¢babysitters, housekeepers and other visitors do not have unwanted access to the network Conclusion You've studied the analysis and are ready to make your decision. Bottom line, then, which is better – wired or wireless? The table below summarizes the main criteria we've considered in this article. If you are very cost-conscious, need maximum performance of your home system, and don't care much about mobility, then a wired Ethernet LAN is probably right for you. If on the other hand, cost is less of an issue, you like being an early adopter of leading-edge technologies, and you are really concerned about the task of wiring your home or small business with Ethernet cable, then you should certainly consider a wireless LAN. Wired vs Wireless Wired Wireless Installationmoderate difficultyeasier, but beware interference Cost less more Reliability High Reasonably high Performancevery good good Security reasonably good reasonably good Mobility limited outstanding

What Is Glass Transition Temperature