Greek Mythology and Achilles Introduction Essay Example for Free

Greek Mythology and Achilles Introduction Essay Introduction Once upon a time, long ago there was a marvelous battle called the Trojan War, but before hand, there lived a Greek god named Peleus who extracted love for the Sea goddess Thetis. As time passed, they became one, so they thought why not form our love in to a child. When their child was born, Thetis dipped him into the river styx which was in the underworld (Achilles). Thus made him immortal and his name was Achilles. When Thetis dipped Achilles in to the underworld, she held him from his heel, this spot remained vulnerable, (Achilles). Meaning it was the only spot in his body that remained mortal. Achilles’ parents knew that he would become the greatest fighter ever lived, (Gill). So Achilles knew that he would end up fighting in the Trojan War. Personal Qualities Achilles was a great warrior who possessed many unique qualities; for one, he was immortal. He was a man who was known for his incredible strength, fighting ability and his intimidating armor. Some of his other main qualities were that he was part human, past super natural, (Achilles). He was very courageous, brave, and also strong. He used his strength and bravery to kill Hector, king of the Trojans, (Achilles 1). Achilles was also very well known for his helmet, which was gold with red horse tips above it. His armor would always be recognized in battle. Achilles had many weapons, but his two main battle pieces were his short sword and spere, (Gill). When fighting, Achilles showed no mercy. When he killed Hector, king of Troy, he tied Troy’s king to the back of his chariot and dragged his corpse around the city walls for twelve days, (Gill). Achilles is unique, and the qualities he possessed are too. Personal Struggles and Achievements Achilles was a great man, he seemed perfect, but every great fighter has a  weakness and for Achilles it was his heel, (Achilles 1). Although Achilles has weaknesses, that did not stop him from his many achievements that were successful. Prophecies said, â€Å"Troy would only win if Achilles was on his side†, (Gill). Achilles was sent to kill Hector in the Trojan Warm so he did and came out successful. Sadly, in the war an arrow that was shot from the brother of Hector, Paris, landed in Achilles’ heel. Being the only vulnerable spot in his body, he died at Troy while still a young man, (Gill). Conclusion Achilles was a great leader and always led in battle. He was born and became one of the best fighters ever lived, (Achilles). Achilles was and will be remembered as â€Å"A hero with a weakness†, (Achilles 1). He was an immortal man with a great fighting ability, also a leader who showed courage and left his footprint, literally. Works Cited â€Å"Achilles†. Myth Encyclopedia.J rank.Web. March 20, 2011 Gill, N.S. â€Å"Achilles- Trojan War Hero Achilles† About.com.2011.INT.Friday, 08 April 2011. â€Å"Achilles†.GreekMythology Edition.Search, 2011.web.7Mar.2011.

Underwater Acoustic Sensor Network (UASN)

Underwater Acoustic Sensor Network (UASN) CHAPTER1: Introduction Most of the earth surface is composed of water including fresh water from river, lakes etc and salt water from the sea. There are still many un-explored areas for such places. This needs significant research efforts and good communication systems. Wireless sensor network in aqueous medium has the ability to explore the underwater environment in details. For all applications of underwater, a good communication system as well as an effective routing protocol is needed. This will enable the underwater devices to communicate precisely. Underwater propagation speed varies with temperature, salinity and depth. By varying the underwater propagation speed at different depth, two scenarios can be achieved accurately namely: shallow and deep water. Shallow water consists of depth less than 200m and cylinder spreading. Deep water consists of depth greater or equal to 200 m and spherical spreading. In both shallow and deep water, different ambient noise and different spreading factor is applied. CHAPTER 2: Study of Underwater Acoustic Sensor Network (UASN) Application of UASN Wireless sensor network in aqueous medium also known as underwater sensor network has enabled a broad range of applications including: Environmental Monitoring Underwater sensor network can be used to monitor pollution like chemical, biological such as tracking of fish or micro-organisms, nuclear and oil leakage pollutions in bays, lakes or rivers [1]. Underwater sensor network can also be used to improve weather forecast, detect climate change, predict the effect of human activities on marine ecosystems, ocean currents and temperature change e.g. the global warming effect to ocean. Under Ocean Exploration Exploring minerals, oilfields or reservoir, determine routes for laying undersea cables and exploration valuable minerals can be done with such underwater sensor network. Disaster Prevention Sensor network that measure seismic activity from remote locations can provide tsunami warning to coastal areas, or study the effects of submarine earthquakes (seaquakes) [2] Equipment Monitoring Long-term equipment monitoring may be done with pre-installed infrastructure. Short-term equipment monitoring shares many requirements of long-term seismic monitoring, including the need for wireless (acoustic) communication, automatic configuration into a multihop network, localization (and hence time synchronization), and energy efficient operation Mine Reconnaissance By using acoustic sensors and optical sensors together, mine detection can be accomplished quickly and effectively. Assisted Monitoring Sensor can be used to discover danger on the seabed, locate dangerous rocks or shoals in shallow waters, mooring position, submerged wrecks and to perform bathymetry profiling. Information collection The main goal of communication network is the exchange of information inside the network and outside the network via a gateway or switch center. This application is used to share information among nodes and autonomous underwater vehicles. Characteristic of UASN Underwater Acoustic Networks (UANs), including but not limited to, Underwater Acoustic Sensor Networks (UASNs) and Autonomous Underwater Vehicle Networks (AUVNs) , are defined as networks composed of more than two nodes, using acoustic signals to communicate, for the purpose of underwater applications. UASNs and AUVNs are two important kinds of UANs. The former is composed of many sensor nodes, mostly for a monitoring purpose. The nodes are usually without or with limited capacity to move. The latter is composed of autonomous or unmanned vehicles with high mobility, deployed for applications that need mobility, e.g., exploration. An UAN can be an UASN, or an AUVN, or a combination of both. Acoustic communications, on the other hands, is defined as communication methods from one point to another by using acoustic signals. Network structure is not formed in acoustic point-to-point communications. Sound travels best through the water in comparison with electromagnetic waves and optical signals. Acoustic signal is sound signal waveform, usually produced by sonar for underwater applications. Acoustic signal processing extracts information from acoustic signals in the presence of noise and uncertainty. Underwater acoustic communications are mainly influenced by path loss, noise, multi-path, Doppler spread, and high and variable propagation delay. All these factors determine the temporal and spatial variability of the acoustic channel, and make the available bandwidth of the Underwater Acoustic channel (UW-A) limited and dramatically dependent on both range and frequency. Long-range systems that operate over several tens of kilometers may have a bandwidth of only a few kHz, while a short-range system operating over several tens of meters may have more than a hundred kHz bandwidth. These factors lead to low bit rate. Underwater acoustic communication links can be classified according to their range as very long, long, medium, short, and very short links. Acoustic links are also roughly classified as vertical and horizontal, according to the direction of the sound ray. Their propagation characteristics differ consistently, especially with respect to time dispersion, multi-path spreads, and delay variance. Acoustic signal is the only physical feasible tool that works in underwater environment. Compared with it, electromagnetic wave can only travel in water with short distance due to the high attenuation and absorption effect in underwater environment. It is found that the absorption of electromagnetic energy in sea water is about 45Ãâ€" ?f dB per kilometer, where f is frequency in Hertz; In contrast, the absorption of acoustic signal over most frequencies of interest is about three orders of magnitude lower [40]. Hereafter the factors that influence acoustic communications is analyzed in order to state the challenges posed by the underwater channels for underwater sensor networking. These include: Path loss Attenuation is mainly provoked by absorption due to conversion of acoustic energy into heat, which increases with distance and frequency. It is also caused by scattering a reverberation (on rough ocean surface and bottom), refraction, and dispersion (due to the displacement of the reflection point caused by wind on the surface). Water depth plays a key role in determining the attenuation. Geometric Spreading is the spreading of sound energy as a result of the expansion of the wavefronts. It increases with the propagation distance and is independent of frequency. There are two common kinds of geometric spreading: spherical (omni-directional point source), and cylindrical (horizontal radiation only). Noise Man made noise is mainly caused by machinery noise (pumps, reduction gears, power plants, etc.), and shipping activity (hull fouling, animal life on hull, cavitations), especially in areas encumbered with heavy vessel traffic. Ambient Noise is related to hydrodynamics (movement of water including tides, current, storms, wind, rain, etc.), seismic and biological phenomena. Multi-path Multi-path propagation may be responsible for severe degradation of the acoustic communication signal, since it generates Inter-Symbol Interference (ISI). The multi-path geometry depends on the link configuration. Vertical channels are characterized by little time dispersion, whereas horizontal channels may have extremely long multi-path spreads. The extent of the spreading is a strong function of depth and the distance between transmitter and receiver. High delay and delay variance The propagation speed in the UW-A channel is five orders of magnitude lower than in the radio channel. This large propagation delay (0.67 s/km) can reduce the throughput of the system considerably. The very high delay variance is even more harmful for efficient protocol design, as it prevents from accurately estimating the round trip time (RTT), which is the key parameter for many common communication protocols. Doppler spread The Doppler frequency spread can be significant in UW-A channels, causing degradation in the performance of digital communications: transmissions at a high data rate because many adjacent symbols to interfere at the receiver, requiring sophisticated signal processing to deal with the generated ISI. The Doppler spreading generates: a simple frequency translation, which is relatively easy for a receiver to compensate for a continuous spreading of frequencies, which constitutes a non-shifted signal, which is more difficult for a receiver to compensate for. If a channel has a Doppler spread with bandwidth B and a signal has symbol duration T, then there are approximately BT uncorrelated samples of its complex envelope. When BT is much less than unity, the channel is said to be under spread and the effects of the Doppler fading can be ignored, while, if greater than unity, it is overspread. Most of the described factors are caused by the chemical-physical properties of the water medium such as temperature, salinity and density, and by their spatio-temporal variations. These variations, together with the wave guide nature of the channel, because the acoustic channel to be temporally and spatially variable. In particular, the horizontal channel is by far more rapidly varying than the vertical channel, in both deep and shallow water. CHAPTER 3: Network Architecture Underwater sensor nodes: The underwater sensor nodes are deployed on the sea floor anchored to the ocean bottom [32]. The sensors are equipped with floating buoys to push the nodes upwards, thus they are relatively stationary nodes [3]. Using acoustic links, they relay data to underwater sink directly or via multi-hop path. Underwater sink nodes: Underwater sink nodes take charge of collecting data of underwater sensors deployed on the ocean bottom and then send to the surface sink node. They may be equipped with vertical and horizontal acoustic transducers. The horizontal transceiver is used to collect the sensors data and the vertical transceiver provides transmitting link between underwater sink and the surface sink node. Surface sink node: Surface sink node is attached on a floating buoy with satellite, radio frequency (RF) or cell phone technology to transmit data to shore in real time. 2D Model A reference architecture for two-dimensional underwater networks is shown in Figure. 1. A group of sensor nodes are anchored to the deep of the ocean. Underwater sensor nodes are interconnected to one or more underwater gateways by means of wireless acoustic links. Underwater-gateways are network devices in charge of relaying data from the ocean bottom network to a surface station. To achieve this objective, they are equipped with two acoustic transceivers, namely a vertical and a horizontal transceiver. The horizontal transceiver is used by the underwater-gateway to communicate with the sensor nodes in order to: send commands and configuration data to the sensors (underwater -gateway to sensors); collect monitored data (sensors to underwater -gateway). The vertical link is used by the underwater -gateways to relay data to a surface station. In deep water applications, vertical transceivers must be long range transceivers. The surface station is equipped with an acoustic transceiver that is able to handle multiple parallel communications with the deployed underwater -gateways. It is also endowed with a long range RF and/or satellite transmitter to communicate with the onshore sink (os-sink) and/or to a surface sink (s-sink). In shallow water, bottom-deployed sensors/modems may directly communicate with the surface buoy, with no specialized bottom node (underwater -gateway). 3D Model Three-dimensional underwater networks are used to detect and observe phenomena that cannot be adequately observed by means of ocean bottom sensor nodes, i.e., to perform cooperative sampling of the 3D ocean environment. In three-dimensional underwater networks, sensor nodes float at different depths to observe a phenomenon. In this architecture, given in Figure 2, each sensor is anchored to the ocean bottom and equipped with a floating buoy that can be inflated by a pump. The buoy pushes the sensor towards the ocean surface. The depth of the sensor can then be regulated by adjusting the length of the wire that connects the sensor to the anchor, by means of an electronically controlled engine that resides on the sensor. Sensing and communication coverage in a 3D environment are rigorously investigated in [8]. The diameter, minimum and maximum degree of the reachability graph that describes the network are derived as a function of the communication range, while different degrees of cov erage for the 3D environment are characterized as a function of the sensing range. 3D Model with AUV The above figure represents the third type of network architecture which consist of sensor nodes and Autonomous Underwater Vehicles (AUV) which act as mobile sensor nodes for ocean monitoring, underwater resource study, etc. CHAPTER 4: Differences between underwater and terrestrial Sensor Network An underwater acoustic channel is different from a ground-based radio channel from many aspects, including: Bandwidth is extremely limited. The attenuation of acoustic signal increases with frequency and range [6] [10]. Consequently, the feasible band is extremely small. For example, a short range system operating over several tens of meters may have available bandwidth of a hundred kHz; a medium-range system operating over several kilometers has a bandwidth on the order of ten kHz; and a long-range system operating over several tens of kilometers is limited to only a few kHz of bandwidth [11]. Propagation delay is long. The transmission speed of acoustic signals in salty water is around 1500 meter/s [22], which is a difference of five orders of magnitude lower than the speed of electromagnetic wave in free space. Correspondently, propagation delay in an underwater channel becomes significant. This is one of the essential characteristics of underwater channels and has profound implications on localization and time synchronization. The channel impulse response is not only spatially varied but also temporarily varied. The channel characteristics vary with time and highly depend on the location of the transmitter and receiver. The fluctuation nature of the channel causes the received signals easily distorted. There are two types of propagation paths: macro-multipaths, which are the deterministic propagation paths; and micro-multipath, which is a random signal fluctuation. The macro-multipaths are caused by both reflection at the boundaries (bottom, surface and any object in the water) and bending. Inter- Symbol Interference (ISI) thus occurs. Compared with the spread of its ground-based counterpart, which is on the order of several symbol intervals, ISI spreading in an underwater acoustic channel is several tens or hundred of symbol intervals for moderate to high data rate in the horizontal channel. Micro-multipath fluctuations are mainly caused by surface wave, which contributes the most to the time variability of shallow water channel. In deep water, internal waves impact the single-path random fluctuations [12][13]. Probability of bit error is much higher and temporary loss of connectivity (shadow zone) sometimes occurs, due to the extreme characteristics of the channel. Cost. While terrestrial sensor nodes are expected to become increasingly inexpensive, underwater sensors are expensive devices. This is especially due to the more complex underwater transceivers and to the hardware protection needed in the extreme underwater environment. Also, because of the low economy of scale caused by a small relative number of suppliers, underwater sensors are characterized by high cost. Deployment. While terrestrial sensor networks are densely deployed, in underwater, the deployment is generally more sparse. Power. The power needed for acoustic underwater communications is higher than in terrestrial radio communications because of the different physical layer technology (acoustic vs. RF waves), the higher distances, and more complex signal processing techniques implemented at the receivers to compensate for the impairments of the channel. Memory. While terrestrial sensor nodes have very limited storage capacity, underwater-sensors may need to be able to do some data caching as the underwater channel may be intermittent. Spatial Correlation. While the readings from terrestrial sensors are often correlated, this is more unlikely to happen in underwater networks due to the higher distance among sensors. CHAPTER 5: Layered of UASN The underwater architecture network consists of five layers, application, transport, network, data link and physical layer as shown in the figure below. As typical underwater systems have limited processing capability, the protocol has been kept as simple as possible without significantly compromising performance. The underwater sensor network specifications currently do not include any recommendations for authentication and encryption. These may be easily implemented at the application layer or via a spreading scheme at the physical layer. Each layer is described by a SAPI. The SAPI is defined in terms of messages being passed to and from the layer. The clients (usually higher layers) of a layer invoke the layer via a request (REQ). The layer responds to each REQ by a response (RSP). Errors are reported via an ERR RSP with error codes. If the layer needs to send unsolicited messages to the client, it does so via a notification (NTF). A layer communicates logically with its peer layer via protocol data units (PDU). As the peer-to-peer communication is symmetric, a layer may send a REQ PDU to its peer layer at any time. It would optionally respond to such a PDU with a RSP PDU. This is logically depicted in Figure below It may be desirable in some cases, that non-neighboring layers communicate with each other to achieve cross-layer optimization. This may be implemented by allowing REQ and RSP PDUs between any two layers in the protocol stack. The underwater sensor network specifications define detailed message structures for all SAPI messages. These message structures include message identifiers, data formats to be used, parameters and their possible values Physical layer The physical layer provides framing, modulation and error correction capability (via FEC). It provides primitives for sending and receiving packets. It may also provide additional functionality such as parameter settings, parameter recommendation, carrier sensing, etc. At first underwater channel development was based on non-coherent frequency shift keying (FSK) modulation, since it relies on energy detection. Thus, it does not require phase tracking, which is a very difficult task mainly because of the Doppler-spread in the underwater acoustic channel. Although non-coherent modulation schemes are characterized by high power efficiency, their low bandwidth efficiency makes them unsuitable for high data rate multiuser networks. Hence, coherent modulation techniques have been developed for long-range, high-throughput systems. In the last years, fully coherent modulation techniques, such as phase shift keying (PSK) and quadrature amplitude modulation (QAM), have become practical due to the availability of powerful digital processing. Channel equalization techniques are exploited to leverage the effect of the inter-symbol interference (ISI), instead of trying to avoid or suppress it. Decision-feedback equalizers (DFEs) track the complex, relatively slowly varying channel response and thus provide high throughput when the channel is slowly varying. Conversely, when the channel varies faster, it is necessary to combine the DFE with a Phase Locked Loop (PLL) [9], which estimates and compensates for the phase offset in a rapid, stable manner. The use of decision feedback equalization and phase-locked loops is driven by the complexity and time variability of ocean channel impulse responses. Differential phase shift keying (DPSK) serves as an intermediate solution between incoherent and fully coherent systems in terms of bandwidth efficiency. DPSK encodes information relative to the previous symbol rather than to an arbitrary fixed reference in the signal phase and may be referred to as a partially coherent modulation. While this strategy substantially alleviates carrier phase-tracking requirements, the penalty is an increased error probability over PSK at an equivalent data rate. Another promising solution for underwater communications is the orthogonal frequency division multiplexing (OFDM) spread spectrum technique, which is particularly efficient when noise is spread over a large portion of the available bandwidth. OFDM is frequently referred to as multicarrier modulation because it transmits signals over multiple sub-carriers simultaneously. In particular, sub-carriers that experience higher SNR, are allotted with a higher number of bits, whereas less bits are allotted to sub-carriers experiencing attenuation, according to the concept of bit loading, which requires channel estimation. Since the symbol duration for each individual carrier increases, OFDM systems perform robustly in severe multi-path environments, and achieve a high spectral efficiency. Many of the techniques discussed above require underwater channel estimation, which can be achieved by means of probe packets [17]. An accurate estimate of the channel can be obtained with a high probing rate and/or with a large probe packet size, which however result in high overhead, and in the consequent drain of channel capacity and energy. Data link layer (MAC layer) The data link layer provides single hop data transmission capability; it will not be able to transmit a packet successfully if the destination node is not directly accessible from the source node. It may include some degree of reliability. It may also provide error detection capability (e.g. CRC check). In case of a shared medium, the data link layer must include the medium access control (MAC) sub-layer. Frequency division multiple access (FDMA) is not suitable for underwater sensor network due to the narrow bandwidth in underwater acoustic channels and the vulnerability of limited band systems to fading and multipath. Time division multiple access (TDMA) shows limited bandwidth efficiency because of the long time guards required in the underwater acoustic channel. In fact, long time guards must be designed to account for the large propagation delay and delay variance of the underwater channel in order to minimize packet collisions from adjacent time slots. Moreover, the variable delay makes it very challenging to realize a precise synchronization, with a common timing reference, which is required for TDMA. Carrier sense multiple access (CSMA) prevents collisions with the ongoing transmission at the transmitter side. To prevent collisions at the receiver side, however, it is necessary to add a guard time between transmissions dimensioned according to the maximum propagation delay in the network. This makes the protocol dramatically inefficient for underwater acoustic sensor network. The use of contention-based techniques that rely on handshaking mechanisms such as RTS/ CTS in shared medium access is impractical in underwater, for the following reasons: large delays in the propagation of RTS/CTS control packets lead to low throughput; due to the high propagation delay of underwater acoustic channels, when carrier sense is used, as in 802.11, it is more likely that the channel be sensed idle while a transmission is ongoing, since the signal may not have reached the receiver yet; the high variability of delay in handshaking packets makes it impractical to predict the start and finish time of the transmissions of other stations. Thus, collisions are highly likely to occur. Code division multiple access (CDMA) is quite robust to frequency selective fading caused by underwater multi-paths, since it distinguishes simultaneous signals transmitted by multiple devices by means of pseudo-noise codes that are used for spreading the user signal over the entire available band. CDMA allows reducing the number of packet retransmissions, which results in decreased battery consumption and increased network throughput. In conclusion, although the high delay spread which characterizes the horizontal link in underwater channels makes it difficult to maintain synchronization among the stations, especially when orthogonal code techniques are used [17], CDMA is a promising multiple access technique for underwater acoustic networks. This is particularly true in shallow water, where multi-paths and Doppler- spreading plays a key role in the communication performance. Network layer (Routing) The network layer is in charge of determining the path between a source (the sensor that samples a physical phenomenon) and a destination node (usually the surface station). In general, while many impairments of the underwater acoustic channel are adequately addressed at the physical and data link layers, some other characteristics, such as the extremely long propagation delays, are better addressed at the network layer. Basically, there are two methods of routing. The first one is virtual circuit routing and the second one is packet-switch routing. In virtual circuit routing, the networks use virtual circuits to decide on the path at the beginning of the network operation. Virtual-circuit-switch routing protocols can be a better choice for underwater acoustic networks. The reasons are: Underwater acoustic networks are typical asymmetric instead of symmetric. However, packet switched routing protocols are proposed for symmetric network architecture; Virtual-circuit-switch routing protocols work robust against link failure, which is critical in underwater environment; and Virtual-circuit-switch routing protocols have less signal overhead and low latency, which are needed for underwater acoustic channel environment. However, virtual-circuit-switch routing protocols usually lack of flexibility. In packet-switch routing, every node that is part of the transmission makes its own routing decision, i.e., decides its next hop to relay the packet. Packet-switch routing can be further classified into Proactive routing, Reactive and geographical routing protocols. Most routing protocols for ground-based wireless networks are packet-switch based. Proactive routing protocols attempt to minimize the message latency by maintaining up-to-date routing information at all times from each node to any other node. It broadcasts control packets that contain routing table information. Typical protocols include Destination Sequence Distance Vector (DSDV) [28] and Temporally Ordered Routing Algorithm (TORA). However, proactive routing protocols provoke a large signaling overhead to establish routes for the first time and each time the network topology changes. It may not be a good fit in underwater environment due to the high probability of link failure and extremely limited bandwidth there. Reactive routing protocols only initiate a route discovery process upon request. Correspondently, each node does not need to maintain a sizable look-up table for routing. This kind of routing protocols is more suitable for dynamic environment like ad hoc wireless networks. Typical protocol examples are Ad hoc On-demand Distance Vector (AODV) [23], and Dynamic Source Routing (DSR) [27]. The shortage of reactive routing protocols is its high latency to establish routing. Similar to its proactive counterpart, flooding of control packets to establish paths is needed, which brings significant signal overhead. The high latency could become much deteriorated in underwater environment because of the much slower propagation speed of acoustic signal compared with the radio wave in the air. Geographic routing (also called georouting or position-based routing) is a routing principle that relies on geographic position information. It is mainly proposed for wireless networks and based on the idea that the source sends a message to the geographic location of the destination instead of using the network address. Geographic routing requires that each node can determine its own location and that the source is aware of the location of the destination. With this information a message can be routed to the destination without knowledge of the network topology or a prior route discovery. Transport layer A transport layer protocol is needed in underwater sensor network not only to achieve reliable collective transport of event features, but also to perform flow control and congestion control. The primary objective is to save scarce sensor resources and increase the network efficiency. A reliable transport protocol should guarantee that the applications be able to correctly identify event features estimated by the sensor network. Congestion control is needed to prevent the network from being congested by excessive data with respect to the network capacity, while flow control is needed to avoid that network devices with limited memory are overwhelmed by data transmissions. Most existing TCP implementations are unsuited for the underwater environment, since the flow control functionality is based on a window- based mechanism that relies on an accurate esteem of the round trip time (RTT), which is twice the end-to-end delay from source to destination. Rate-based transport protocols seem also unsuited for this challenging environment. They still rely on feedback control messages sent back by the destination to dynamically adapt the transmission rate, i.e., to decrease the transmission rate when packet loss is experienced or to increase it otherwise. The high delay and delay variance can thus cause instability in the feedback control. Furthermore, due to the unreliability of the acoustic channel, it is necessary to distinguish between packet losses due to the high bit error rate of the acoustic channel, from those caused by packets being dropped from the queues of sensor nodes due to network congestion. In terrestrial, assume that congestion is the only cause for packet loss and the solution lies on decreasing the transmission rate, but in underwater sensor network if the packet loss is due to bad channel then the transmission rate should not be decreased to preserve throughput efficiency. Transport layer functionalities can be tightly integrated with data link layer functionalities in a cross-layer module. The purpose of such an integrated module is to make the information about the condition of the variable underwater channel available also at the transport layer. In fact, usually the state of the channel is known only at the physical and channel access sub-layers, while the design principle of layer separation makes this information transparent to the higher layers. This integration allows maximizing the Underwater Acoustic Sensor Network (UASN) Underwater Acoustic Sensor Network (UASN) CHAPTER1: Introduction Most of the earth surface is composed of water including fresh water from river, lakes etc and salt water from the sea. There are still many un-explored areas for such places. This needs significant research efforts and good communication systems. Wireless sensor network in aqueous medium has the ability to explore the underwater environment in details. For all applications of underwater, a good communication system as well as an effective routing protocol is needed. This will enable the underwater devices to communicate precisely. Underwater propagation speed varies with temperature, salinity and depth. By varying the underwater propagation speed at different depth, two scenarios can be achieved accurately namely: shallow and deep water. Shallow water consists of depth less than 200m and cylinder spreading. Deep water consists of depth greater or equal to 200 m and spherical spreading. In both shallow and deep water, different ambient noise and different spreading factor is applied. CHAPTER 2: Study of Underwater Acoustic Sensor Network (UASN) Application of UASN Wireless sensor network in aqueous medium also known as underwater sensor network has enabled a broad range of applications including: Environmental Monitoring Underwater sensor network can be used to monitor pollution like chemical, biological such as tracking of fish or micro-organisms, nuclear and oil leakage pollutions in bays, lakes or rivers [1]. Underwater sensor network can also be used to improve weather forecast, detect climate change, predict the effect of human activities on marine ecosystems, ocean currents and temperature change e.g. the global warming effect to ocean. Under Ocean Exploration Exploring minerals, oilfields or reservoir, determine routes for laying undersea cables and exploration valuable minerals can be done with such underwater sensor network. Disaster Prevention Sensor network that measure seismic activity from remote locations can provide tsunami warning to coastal areas, or study the effects of submarine earthquakes (seaquakes) [2] Equipment Monitoring Long-term equipment monitoring may be done with pre-installed infrastructure. Short-term equipment monitoring shares many requirements of long-term seismic monitoring, including the need for wireless (acoustic) communication, automatic configuration into a multihop network, localization (and hence time synchronization), and energy efficient operation Mine Reconnaissance By using acoustic sensors and optical sensors together, mine detection can be accomplished quickly and effectively. Assisted Monitoring Sensor can be used to discover danger on the seabed, locate dangerous rocks or shoals in shallow waters, mooring position, submerged wrecks and to perform bathymetry profiling. Information collection The main goal of communication network is the exchange of information inside the network and outside the network via a gateway or switch center. This application is used to share information among nodes and autonomous underwater vehicles. Characteristic of UASN Underwater Acoustic Networks (UANs), including but not limited to, Underwater Acoustic Sensor Networks (UASNs) and Autonomous Underwater Vehicle Networks (AUVNs) , are defined as networks composed of more than two nodes, using acoustic signals to communicate, for the purpose of underwater applications. UASNs and AUVNs are two important kinds of UANs. The former is composed of many sensor nodes, mostly for a monitoring purpose. The nodes are usually without or with limited capacity to move. The latter is composed of autonomous or unmanned vehicles with high mobility, deployed for applications that need mobility, e.g., exploration. An UAN can be an UASN, or an AUVN, or a combination of both. Acoustic communications, on the other hands, is defined as communication methods from one point to another by using acoustic signals. Network structure is not formed in acoustic point-to-point communications. Sound travels best through the water in comparison with electromagnetic waves and optical signals. Acoustic signal is sound signal waveform, usually produced by sonar for underwater applications. Acoustic signal processing extracts information from acoustic signals in the presence of noise and uncertainty. Underwater acoustic communications are mainly influenced by path loss, noise, multi-path, Doppler spread, and high and variable propagation delay. All these factors determine the temporal and spatial variability of the acoustic channel, and make the available bandwidth of the Underwater Acoustic channel (UW-A) limited and dramatically dependent on both range and frequency. Long-range systems that operate over several tens of kilometers may have a bandwidth of only a few kHz, while a short-range system operating over several tens of meters may have more than a hundred kHz bandwidth. These factors lead to low bit rate. Underwater acoustic communication links can be classified according to their range as very long, long, medium, short, and very short links. Acoustic links are also roughly classified as vertical and horizontal, according to the direction of the sound ray. Their propagation characteristics differ consistently, especially with respect to time dispersion, multi-path spreads, and delay variance. Acoustic signal is the only physical feasible tool that works in underwater environment. Compared with it, electromagnetic wave can only travel in water with short distance due to the high attenuation and absorption effect in underwater environment. It is found that the absorption of electromagnetic energy in sea water is about 45Ãâ€" ?f dB per kilometer, where f is frequency in Hertz; In contrast, the absorption of acoustic signal over most frequencies of interest is about three orders of magnitude lower [40]. Hereafter the factors that influence acoustic communications is analyzed in order to state the challenges posed by the underwater channels for underwater sensor networking. These include: Path loss Attenuation is mainly provoked by absorption due to conversion of acoustic energy into heat, which increases with distance and frequency. It is also caused by scattering a reverberation (on rough ocean surface and bottom), refraction, and dispersion (due to the displacement of the reflection point caused by wind on the surface). Water depth plays a key role in determining the attenuation. Geometric Spreading is the spreading of sound energy as a result of the expansion of the wavefronts. It increases with the propagation distance and is independent of frequency. There are two common kinds of geometric spreading: spherical (omni-directional point source), and cylindrical (horizontal radiation only). Noise Man made noise is mainly caused by machinery noise (pumps, reduction gears, power plants, etc.), and shipping activity (hull fouling, animal life on hull, cavitations), especially in areas encumbered with heavy vessel traffic. Ambient Noise is related to hydrodynamics (movement of water including tides, current, storms, wind, rain, etc.), seismic and biological phenomena. Multi-path Multi-path propagation may be responsible for severe degradation of the acoustic communication signal, since it generates Inter-Symbol Interference (ISI). The multi-path geometry depends on the link configuration. Vertical channels are characterized by little time dispersion, whereas horizontal channels may have extremely long multi-path spreads. The extent of the spreading is a strong function of depth and the distance between transmitter and receiver. High delay and delay variance The propagation speed in the UW-A channel is five orders of magnitude lower than in the radio channel. This large propagation delay (0.67 s/km) can reduce the throughput of the system considerably. The very high delay variance is even more harmful for efficient protocol design, as it prevents from accurately estimating the round trip time (RTT), which is the key parameter for many common communication protocols. Doppler spread The Doppler frequency spread can be significant in UW-A channels, causing degradation in the performance of digital communications: transmissions at a high data rate because many adjacent symbols to interfere at the receiver, requiring sophisticated signal processing to deal with the generated ISI. The Doppler spreading generates: a simple frequency translation, which is relatively easy for a receiver to compensate for a continuous spreading of frequencies, which constitutes a non-shifted signal, which is more difficult for a receiver to compensate for. If a channel has a Doppler spread with bandwidth B and a signal has symbol duration T, then there are approximately BT uncorrelated samples of its complex envelope. When BT is much less than unity, the channel is said to be under spread and the effects of the Doppler fading can be ignored, while, if greater than unity, it is overspread. Most of the described factors are caused by the chemical-physical properties of the water medium such as temperature, salinity and density, and by their spatio-temporal variations. These variations, together with the wave guide nature of the channel, because the acoustic channel to be temporally and spatially variable. In particular, the horizontal channel is by far more rapidly varying than the vertical channel, in both deep and shallow water. CHAPTER 3: Network Architecture Underwater sensor nodes: The underwater sensor nodes are deployed on the sea floor anchored to the ocean bottom [32]. The sensors are equipped with floating buoys to push the nodes upwards, thus they are relatively stationary nodes [3]. Using acoustic links, they relay data to underwater sink directly or via multi-hop path. Underwater sink nodes: Underwater sink nodes take charge of collecting data of underwater sensors deployed on the ocean bottom and then send to the surface sink node. They may be equipped with vertical and horizontal acoustic transducers. The horizontal transceiver is used to collect the sensors data and the vertical transceiver provides transmitting link between underwater sink and the surface sink node. Surface sink node: Surface sink node is attached on a floating buoy with satellite, radio frequency (RF) or cell phone technology to transmit data to shore in real time. 2D Model A reference architecture for two-dimensional underwater networks is shown in Figure. 1. A group of sensor nodes are anchored to the deep of the ocean. Underwater sensor nodes are interconnected to one or more underwater gateways by means of wireless acoustic links. Underwater-gateways are network devices in charge of relaying data from the ocean bottom network to a surface station. To achieve this objective, they are equipped with two acoustic transceivers, namely a vertical and a horizontal transceiver. The horizontal transceiver is used by the underwater-gateway to communicate with the sensor nodes in order to: send commands and configuration data to the sensors (underwater -gateway to sensors); collect monitored data (sensors to underwater -gateway). The vertical link is used by the underwater -gateways to relay data to a surface station. In deep water applications, vertical transceivers must be long range transceivers. The surface station is equipped with an acoustic transceiver that is able to handle multiple parallel communications with the deployed underwater -gateways. It is also endowed with a long range RF and/or satellite transmitter to communicate with the onshore sink (os-sink) and/or to a surface sink (s-sink). In shallow water, bottom-deployed sensors/modems may directly communicate with the surface buoy, with no specialized bottom node (underwater -gateway). 3D Model Three-dimensional underwater networks are used to detect and observe phenomena that cannot be adequately observed by means of ocean bottom sensor nodes, i.e., to perform cooperative sampling of the 3D ocean environment. In three-dimensional underwater networks, sensor nodes float at different depths to observe a phenomenon. In this architecture, given in Figure 2, each sensor is anchored to the ocean bottom and equipped with a floating buoy that can be inflated by a pump. The buoy pushes the sensor towards the ocean surface. The depth of the sensor can then be regulated by adjusting the length of the wire that connects the sensor to the anchor, by means of an electronically controlled engine that resides on the sensor. Sensing and communication coverage in a 3D environment are rigorously investigated in [8]. The diameter, minimum and maximum degree of the reachability graph that describes the network are derived as a function of the communication range, while different degrees of cov erage for the 3D environment are characterized as a function of the sensing range. 3D Model with AUV The above figure represents the third type of network architecture which consist of sensor nodes and Autonomous Underwater Vehicles (AUV) which act as mobile sensor nodes for ocean monitoring, underwater resource study, etc. CHAPTER 4: Differences between underwater and terrestrial Sensor Network An underwater acoustic channel is different from a ground-based radio channel from many aspects, including: Bandwidth is extremely limited. The attenuation of acoustic signal increases with frequency and range [6] [10]. Consequently, the feasible band is extremely small. For example, a short range system operating over several tens of meters may have available bandwidth of a hundred kHz; a medium-range system operating over several kilometers has a bandwidth on the order of ten kHz; and a long-range system operating over several tens of kilometers is limited to only a few kHz of bandwidth [11]. Propagation delay is long. The transmission speed of acoustic signals in salty water is around 1500 meter/s [22], which is a difference of five orders of magnitude lower than the speed of electromagnetic wave in free space. Correspondently, propagation delay in an underwater channel becomes significant. This is one of the essential characteristics of underwater channels and has profound implications on localization and time synchronization. The channel impulse response is not only spatially varied but also temporarily varied. The channel characteristics vary with time and highly depend on the location of the transmitter and receiver. The fluctuation nature of the channel causes the received signals easily distorted. There are two types of propagation paths: macro-multipaths, which are the deterministic propagation paths; and micro-multipath, which is a random signal fluctuation. The macro-multipaths are caused by both reflection at the boundaries (bottom, surface and any object in the water) and bending. Inter- Symbol Interference (ISI) thus occurs. Compared with the spread of its ground-based counterpart, which is on the order of several symbol intervals, ISI spreading in an underwater acoustic channel is several tens or hundred of symbol intervals for moderate to high data rate in the horizontal channel. Micro-multipath fluctuations are mainly caused by surface wave, which contributes the most to the time variability of shallow water channel. In deep water, internal waves impact the single-path random fluctuations [12][13]. Probability of bit error is much higher and temporary loss of connectivity (shadow zone) sometimes occurs, due to the extreme characteristics of the channel. Cost. While terrestrial sensor nodes are expected to become increasingly inexpensive, underwater sensors are expensive devices. This is especially due to the more complex underwater transceivers and to the hardware protection needed in the extreme underwater environment. Also, because of the low economy of scale caused by a small relative number of suppliers, underwater sensors are characterized by high cost. Deployment. While terrestrial sensor networks are densely deployed, in underwater, the deployment is generally more sparse. Power. The power needed for acoustic underwater communications is higher than in terrestrial radio communications because of the different physical layer technology (acoustic vs. RF waves), the higher distances, and more complex signal processing techniques implemented at the receivers to compensate for the impairments of the channel. Memory. While terrestrial sensor nodes have very limited storage capacity, underwater-sensors may need to be able to do some data caching as the underwater channel may be intermittent. Spatial Correlation. While the readings from terrestrial sensors are often correlated, this is more unlikely to happen in underwater networks due to the higher distance among sensors. CHAPTER 5: Layered of UASN The underwater architecture network consists of five layers, application, transport, network, data link and physical layer as shown in the figure below. As typical underwater systems have limited processing capability, the protocol has been kept as simple as possible without significantly compromising performance. The underwater sensor network specifications currently do not include any recommendations for authentication and encryption. These may be easily implemented at the application layer or via a spreading scheme at the physical layer. Each layer is described by a SAPI. The SAPI is defined in terms of messages being passed to and from the layer. The clients (usually higher layers) of a layer invoke the layer via a request (REQ). The layer responds to each REQ by a response (RSP). Errors are reported via an ERR RSP with error codes. If the layer needs to send unsolicited messages to the client, it does so via a notification (NTF). A layer communicates logically with its peer layer via protocol data units (PDU). As the peer-to-peer communication is symmetric, a layer may send a REQ PDU to its peer layer at any time. It would optionally respond to such a PDU with a RSP PDU. This is logically depicted in Figure below It may be desirable in some cases, that non-neighboring layers communicate with each other to achieve cross-layer optimization. This may be implemented by allowing REQ and RSP PDUs between any two layers in the protocol stack. The underwater sensor network specifications define detailed message structures for all SAPI messages. These message structures include message identifiers, data formats to be used, parameters and their possible values Physical layer The physical layer provides framing, modulation and error correction capability (via FEC). It provides primitives for sending and receiving packets. It may also provide additional functionality such as parameter settings, parameter recommendation, carrier sensing, etc. At first underwater channel development was based on non-coherent frequency shift keying (FSK) modulation, since it relies on energy detection. Thus, it does not require phase tracking, which is a very difficult task mainly because of the Doppler-spread in the underwater acoustic channel. Although non-coherent modulation schemes are characterized by high power efficiency, their low bandwidth efficiency makes them unsuitable for high data rate multiuser networks. Hence, coherent modulation techniques have been developed for long-range, high-throughput systems. In the last years, fully coherent modulation techniques, such as phase shift keying (PSK) and quadrature amplitude modulation (QAM), have become practical due to the availability of powerful digital processing. Channel equalization techniques are exploited to leverage the effect of the inter-symbol interference (ISI), instead of trying to avoid or suppress it. Decision-feedback equalizers (DFEs) track the complex, relatively slowly varying channel response and thus provide high throughput when the channel is slowly varying. Conversely, when the channel varies faster, it is necessary to combine the DFE with a Phase Locked Loop (PLL) [9], which estimates and compensates for the phase offset in a rapid, stable manner. The use of decision feedback equalization and phase-locked loops is driven by the complexity and time variability of ocean channel impulse responses. Differential phase shift keying (DPSK) serves as an intermediate solution between incoherent and fully coherent systems in terms of bandwidth efficiency. DPSK encodes information relative to the previous symbol rather than to an arbitrary fixed reference in the signal phase and may be referred to as a partially coherent modulation. While this strategy substantially alleviates carrier phase-tracking requirements, the penalty is an increased error probability over PSK at an equivalent data rate. Another promising solution for underwater communications is the orthogonal frequency division multiplexing (OFDM) spread spectrum technique, which is particularly efficient when noise is spread over a large portion of the available bandwidth. OFDM is frequently referred to as multicarrier modulation because it transmits signals over multiple sub-carriers simultaneously. In particular, sub-carriers that experience higher SNR, are allotted with a higher number of bits, whereas less bits are allotted to sub-carriers experiencing attenuation, according to the concept of bit loading, which requires channel estimation. Since the symbol duration for each individual carrier increases, OFDM systems perform robustly in severe multi-path environments, and achieve a high spectral efficiency. Many of the techniques discussed above require underwater channel estimation, which can be achieved by means of probe packets [17]. An accurate estimate of the channel can be obtained with a high probing rate and/or with a large probe packet size, which however result in high overhead, and in the consequent drain of channel capacity and energy. Data link layer (MAC layer) The data link layer provides single hop data transmission capability; it will not be able to transmit a packet successfully if the destination node is not directly accessible from the source node. It may include some degree of reliability. It may also provide error detection capability (e.g. CRC check). In case of a shared medium, the data link layer must include the medium access control (MAC) sub-layer. Frequency division multiple access (FDMA) is not suitable for underwater sensor network due to the narrow bandwidth in underwater acoustic channels and the vulnerability of limited band systems to fading and multipath. Time division multiple access (TDMA) shows limited bandwidth efficiency because of the long time guards required in the underwater acoustic channel. In fact, long time guards must be designed to account for the large propagation delay and delay variance of the underwater channel in order to minimize packet collisions from adjacent time slots. Moreover, the variable delay makes it very challenging to realize a precise synchronization, with a common timing reference, which is required for TDMA. Carrier sense multiple access (CSMA) prevents collisions with the ongoing transmission at the transmitter side. To prevent collisions at the receiver side, however, it is necessary to add a guard time between transmissions dimensioned according to the maximum propagation delay in the network. This makes the protocol dramatically inefficient for underwater acoustic sensor network. The use of contention-based techniques that rely on handshaking mechanisms such as RTS/ CTS in shared medium access is impractical in underwater, for the following reasons: large delays in the propagation of RTS/CTS control packets lead to low throughput; due to the high propagation delay of underwater acoustic channels, when carrier sense is used, as in 802.11, it is more likely that the channel be sensed idle while a transmission is ongoing, since the signal may not have reached the receiver yet; the high variability of delay in handshaking packets makes it impractical to predict the start and finish time of the transmissions of other stations. Thus, collisions are highly likely to occur. Code division multiple access (CDMA) is quite robust to frequency selective fading caused by underwater multi-paths, since it distinguishes simultaneous signals transmitted by multiple devices by means of pseudo-noise codes that are used for spreading the user signal over the entire available band. CDMA allows reducing the number of packet retransmissions, which results in decreased battery consumption and increased network throughput. In conclusion, although the high delay spread which characterizes the horizontal link in underwater channels makes it difficult to maintain synchronization among the stations, especially when orthogonal code techniques are used [17], CDMA is a promising multiple access technique for underwater acoustic networks. This is particularly true in shallow water, where multi-paths and Doppler- spreading plays a key role in the communication performance. Network layer (Routing) The network layer is in charge of determining the path between a source (the sensor that samples a physical phenomenon) and a destination node (usually the surface station). In general, while many impairments of the underwater acoustic channel are adequately addressed at the physical and data link layers, some other characteristics, such as the extremely long propagation delays, are better addressed at the network layer. Basically, there are two methods of routing. The first one is virtual circuit routing and the second one is packet-switch routing. In virtual circuit routing, the networks use virtual circuits to decide on the path at the beginning of the network operation. Virtual-circuit-switch routing protocols can be a better choice for underwater acoustic networks. The reasons are: Underwater acoustic networks are typical asymmetric instead of symmetric. However, packet switched routing protocols are proposed for symmetric network architecture; Virtual-circuit-switch routing protocols work robust against link failure, which is critical in underwater environment; and Virtual-circuit-switch routing protocols have less signal overhead and low latency, which are needed for underwater acoustic channel environment. However, virtual-circuit-switch routing protocols usually lack of flexibility. In packet-switch routing, every node that is part of the transmission makes its own routing decision, i.e., decides its next hop to relay the packet. Packet-switch routing can be further classified into Proactive routing, Reactive and geographical routing protocols. Most routing protocols for ground-based wireless networks are packet-switch based. Proactive routing protocols attempt to minimize the message latency by maintaining up-to-date routing information at all times from each node to any other node. It broadcasts control packets that contain routing table information. Typical protocols include Destination Sequence Distance Vector (DSDV) [28] and Temporally Ordered Routing Algorithm (TORA). However, proactive routing protocols provoke a large signaling overhead to establish routes for the first time and each time the network topology changes. It may not be a good fit in underwater environment due to the high probability of link failure and extremely limited bandwidth there. Reactive routing protocols only initiate a route discovery process upon request. Correspondently, each node does not need to maintain a sizable look-up table for routing. This kind of routing protocols is more suitable for dynamic environment like ad hoc wireless networks. Typical protocol examples are Ad hoc On-demand Distance Vector (AODV) [23], and Dynamic Source Routing (DSR) [27]. The shortage of reactive routing protocols is its high latency to establish routing. Similar to its proactive counterpart, flooding of control packets to establish paths is needed, which brings significant signal overhead. The high latency could become much deteriorated in underwater environment because of the much slower propagation speed of acoustic signal compared with the radio wave in the air. Geographic routing (also called georouting or position-based routing) is a routing principle that relies on geographic position information. It is mainly proposed for wireless networks and based on the idea that the source sends a message to the geographic location of the destination instead of using the network address. Geographic routing requires that each node can determine its own location and that the source is aware of the location of the destination. With this information a message can be routed to the destination without knowledge of the network topology or a prior route discovery. Transport layer A transport layer protocol is needed in underwater sensor network not only to achieve reliable collective transport of event features, but also to perform flow control and congestion control. The primary objective is to save scarce sensor resources and increase the network efficiency. A reliable transport protocol should guarantee that the applications be able to correctly identify event features estimated by the sensor network. Congestion control is needed to prevent the network from being congested by excessive data with respect to the network capacity, while flow control is needed to avoid that network devices with limited memory are overwhelmed by data transmissions. Most existing TCP implementations are unsuited for the underwater environment, since the flow control functionality is based on a window- based mechanism that relies on an accurate esteem of the round trip time (RTT), which is twice the end-to-end delay from source to destination. Rate-based transport protocols seem also unsuited for this challenging environment. They still rely on feedback control messages sent back by the destination to dynamically adapt the transmission rate, i.e., to decrease the transmission rate when packet loss is experienced or to increase it otherwise. The high delay and delay variance can thus cause instability in the feedback control. Furthermore, due to the unreliability of the acoustic channel, it is necessary to distinguish between packet losses due to the high bit error rate of the acoustic channel, from those caused by packets being dropped from the queues of sensor nodes due to network congestion. In terrestrial, assume that congestion is the only cause for packet loss and the solution lies on decreasing the transmission rate, but in underwater sensor network if the packet loss is due to bad channel then the transmission rate should not be decreased to preserve throughput efficiency. Transport layer functionalities can be tightly integrated with data link layer functionalities in a cross-layer module. The purpose of such an integrated module is to make the information about the condition of the variable underwater channel available also at the transport layer. In fact, usually the state of the channel is known only at the physical and channel access sub-layers, while the design principle of layer separation makes this information transparent to the higher layers. This integration allows maximizing the

Personal Narrative- Transformation of a Hurting Teen Essay -- Personal

Personal Narrative- Transformation of a Hurting Teen Before I lost my innocence I was care-free, and full of love. But I grew up and my peers began to tease me. â€Å"Am I really fat, ugly, stupid and dorky†? I thought. Every loving part of me was torn apart piece by piece by my young peers like wolves on the prowl. Every fault and every flaw I owned was brought to my attention. This teasing spawned an anger in me so strong that every aspect of my life was destroyed. I began to rebel towards any kind of authority as a way to protect myself. I felt that every breathing thing was out to hurt me. When I was fifteen years of age, this rebellion turned juvenile and I began to get into quite a bit of trouble with my parents and teachers. I was sent to House of Hope, a home for hurting teen...

How Does The ?surround-sound? :: essays research papers

How does the â€Å"surround-sound† technique work?   Ã‚  Ã‚  Ã‚  Ã‚  Surround Sound which was introduced by Dolby Laboratories Inc to position sound around the audience so that the effects within movies would make them feel as though they were really there. The use of directional sound from different points in the room according to their depth, sharpness and clarity was the main goal. Starting off from a standard called Dolby Stereo, two separate channels were introduced, both left and right, so that other speakers could in turn double-up to provide a multitude of left and right channels all around the audience. The input of a effects channel (later called Surround channel) was implemented so that a sense of ambience and spatiality could be experienced from the audience. This surround channel was positioned behind and to the left and right of the audience provided the sound depth that the audio engineers were looking for.   Ã‚  Ã‚  Ã‚  Ã‚  This then gave way to a standard, which was known as Dolby Surround, soon followed by Dolby Surround – Pro Logic. This standard incorporated the original two channels for sound, but had an in-built decoder so that the surround channel, and also a center channel (positioned to the direct front of the audience) could be played back to enhance this surround feeling. A many number of speakers could be connected up to enhance the feeling associated with the different types of audio sources, and in turn provide more depth and realism to the audio source.   Ã‚  Ã‚  Ã‚  Ã‚  Dolby Digital was incorporated into the home cinema as well as movie theatres to provide the ultimate audio reproductive source. The use of individual speaker components positioned around the audience comprising of a front left, front right, surround left, surround right, center, and subwoofer speaker were given their own audio input. This was called Dolby Digital 5.

Teens Parental Friend Essay -- essays research papers

â€Å"It’s okay what you do here. I’m a cool mom.† That’s a quote from the latest teen movie, Mean Girls. Most parents think that being their teen’s best friend is something that will help them understand why teens do what they do. Unfortunately that’s not the case. Parents who give their teens whatever they want at whatever cost are wrong. They are teaching their teen to spoil their own child in the future. They also can start teaching their teen bad habits by not giving them chores to do or making them do homework. When parents become close friends with their teen the role of the authority figure is lost, which causes the teen to become lazy, dependent, and prevents them from succeeding to their highest performance.   Ã‚  Ã‚  Ã‚  Ã‚  Parents who give their teen whatever they want at whatever cost is spoiling their child. Yes, we all understand that parents want to stay active and participate in their teen’s life. If a parent spoils his teen with new clothes, shoes, video games, and money that gives the teen the impression that it’s okay to ask for whatever they want, in reality that’s not possible. The teens have to work for what he wants. In a research 40 percent of parents said that they would buy their child everything they wanted if they could (USA Today). Sampson Lee Blair said, â€Å"Trying to play to every little whim or desire will create problems for the child later in life.† I have to agree. A parent can still be his teen’s friend, but in a different way, a par...

Role of Language and Script in Raising the Religious Revivalism

Role of Language and Script in Raising the Religious Revivalism in Colonial Punjab aYESHA TABBASUM The language played the significant role in the creation of identities among the major communities in pr-parathion India. The Urdu language had developed as a common language among all the communities and was, in the absence of a common religion the North-western Provinces and various part other parts of the subcontinent. I. H. Qureshi, History of the Pakistan,(BCC& Press Karachi, university of karachi2006) 807.Language Controversy between Urdu and Hindi Although it was religion which was the key defining feature of Muslim identity, the Urdu language was an important symbol. For Hindus, except for the religious communities, the symbol of religion had to be played down to avoid alienating other major religious communities. However, despite linguistic pluralism, the Hindi language remained an important symbol in the construction of the Hindu identity for the Hindu community.Tariq Rahman, language and politics in Pakistan,(Karachi, oxford university press 1996) 60 As in colonial Punjab   Hindu patshalas,which taught mantras and basic knowledge of the shastras, Muslims Quran schools, and Sikhs educational institutions which taught the sacred text of Sikhism, the Granth ,and the Gurumukhi Script of the Punjabi language used by Sikhs. The stand read spoken language of north India in the British period was referred to interchangeably as Urdu, Hindi.Paul Brass, language, religion and politics in north India (Cambridge: Cambridge university press, 1974), 129 But its was written in different script: as Urdu was written in Persian script while Hindu community used it in Hindi for general communication purposes was generally written in Devanagri, also known as Nagri. as Urdu was incorporated various Arabic and Persian words while Hindi drew on Sanskrit was cited by Hindu nationalists as â€Å"proof† that Islam was foreign religion in India and there language should b e the language of country.Vickie Langhor, Colonial education system and spread of local religious movements; the cases of British Egypt and Punjab,(Cambridge university press,2005) 174 But it was the fact that Urdu language being used by Hindu community of north Indian. Till 1931 many Hindu in colonial Punjab were literate in Urdu instead of Hindi language. Before the partition of India, during the colonial Punjab Language and script become the major source of division among the major communities of as Hindus –Muslims and Sikhs.Ever since the beginning of the 11th century Northern India was remained under the Muslim rulers. During different periods different Muslims rulers ruled at different times and different dynasties spoke diverse languages as Afghans spoke Pushtu and Turks Turki and the Mughals spoke the Persian, Sikhs of the Punjab A Study of Confrontation and political mobilization, Dr Sarfraz Khawaja, (Islamabad, Pakistan: modern book dept, 1985) 41 As it was the fact that in the period of the later Mughals, Urdu and Persian both languages were the court languages.When British succeeded the subcontinent they continued the same languages as the court languages. Shan Muhammad, the growth of Muslim politics in india1900-1919 (New Delhi, shish publishing house, 1991) 35. These languages were understood, also spoke at large scale, but natives languages were also spoke by the native communities as Hindi, Punjabi Pahari Hindustani. In which Urdu and Hindi both languages were the mixture of native and foreign languages Two sides of one coin Hindi Urdu, or Urdu HindiAs Hindi and Urdu were two names of one language script differentiate between them it called Urdu when it written in perso-Arabic script (both languages were associated with Muslim community) and when written in the Nagari script (associated with Hindu community); there were some lexical and phrasal differences. Yet the two names for one language were frequently used for the same language and its literature segmented into parts largely on the basis of script and religions. S.Settar, Indira BaptistaGupta, Pangs of partition vol ?,(new Delhi: Manohar publisher,2002. ) 34. Punjabi Hindu community used Urdu language as the language of commerce, journalism and administration. Urdu language was also the major language of literary expression not only in Muslim community in Hindu community as well in British Punjab while Punjabi was the spoken language. Atamjit Singh, The languages divide in Punjab South Asian Graduate Research Journal, 9Achadmic of the Punjab new America) Volume 4, No. , spring 1997 Colonial government language policy in Bihar and its after effects Urdu was mixture of Persian, Arabic and Hindi Punjabi. As this spoken language soon become to be written in the Persian and Arabic languages language. Urdu gained the as official language status after the abolishment of the Persian language in various provinces of the northern India so at 1842 lord Lawrence confirme d that â€Å"the use of this language (Urdu) is rapidly spreading among all the ranks and is becoming a lingua Franca† Abid41Till the 2nd half of the 9th century Urdu not only became a dominate language but also symbol of Muslim influence and power But In 1837 Persian language had been replaced by Indian vernaculars and Urdu was introduced as the vernacular of ‘the vast tract of country known as Hindustani language, not only in Bihar and NWP and portions of central as well, However Government did not want personalized Urdu to be used as the vernacular. An order of 19 April 1839 declared:The pleading and proceedings be recorded in lucid intelligible Oordoo, and that the natives ministerial officers†¦ do not merely alternate a hindoostanee for a Persian verb at the end of sentence†¦ Tariq Rahman, language and politics in Pakistan,(Karachi, oxford university press 1996) 62 As various colonial officers discourage again and again Urdu language they were in the favo r to accepting Hindi as the vernacular language of the Hindustani people’s. The director of public instruction stated in his report:    Indo-Persian of the courts has no raisond’etre except as a remnan and reminiscence of mahomedan sovereignty Abid 62.In 1872 sir Gorge Cambell, Lieutenant Governor of Bihar, approved order in which Urdu replaced by Hindi language in the courts of the province and this order was strictly imposed in 1880 by Sir Ashley Eden. Abid 62. As Hindi language was not pure one language but the blend of the many natives’ dialects of north India in its widest perspective it could be assumed that Hindi language spoken in Bihar, Uttar Pradesh, Orissa Madhya Pradesh, Rajasthan and the Colonial Punjab. Dr Sarfraz Khawaga, Sikhs of the Punjab A study of confrontation and political mobilization, (Islamabad: Modern book depot, 1985. 43. As Hindi language had written in Nagari or Devengri script. The Nagri or Devangri alphabet originated sometime in the 11th century AD. initially developed to write Sanskrit it later modified to write   with several other languages. The name Devangri is made up of two Sanskrit words: Deva, which means god, Brahman or celestiai and nagari, which means city. The name is variously translated as ‘script of the city’, ‘heavenly/sacred script of the city’ or [script of the] city of the god or priests’.So for Hindu community Hindi language purged of all Persian and Arabic accretion which served to remind them of Muslim community ascendancy, As Devanagri script had a religious importance for Hindu community since it was the character which Brahmans used and in which Sanskrit books were written. So due to the religious association Hindu community insist to colonial government in various provinces that Urdu written in Persian script must be replaced by the Hindu with its Devanagari script.To fulfill their demand they presented the reason that: (Urdu language was an amal gam of Persian and Arabic languages -and it -and it was forced upon us by our former rulers†¦but it was by no means accepted by the peoples at large†¦no Hindu gentlemen would ever condescend to educate his female in    Urdu language and Persian because the books written   in   these languages are usually obscene. Report by the north western province and qudh provincial committee of education commission, (1884) ,   490. quated by Dr Sarfaz Khawaja op. cit, 72.Pro Hindi –script activities of Hindu community and Muslim response Pro Hindi agitation traveled from Bihar to the other provinces due to the two main reasons as: first when British replaced the Urdu language with Hindi language this decision provide the courage to the Hindu community due to this decision later Bengali Hindu community started protest in Bengal. Secondly then when Fateh chand established committees to press for Hindi language. Pro-Hindi movement quickly spread in    Hindu community of t he north colonial Indian.Then pro Hindi agitation travelled from Bihar, Bengal to other provinces such as NWFP. There was quashed manifestation occurred: a failure to introduce Devanagari in the colonial Punjab and NWFP. Jaswant Singh, Jinnah India-partition-independence (New Delhi: Rupa publisher, 2009. ) 41 Muslim reaction towards Urdu Hindi controversy in colonial Punjab Enforcement of Hindi language became a cause for grievance amongst major religious communities as Hindus and Muslims in various parts of indo-Pak Subcontinent. But in colonial Punjab arose for the very first time in 1882.Paul R. Brass, Language, Religion and Politics in North India (London :Cambridge university press,1974),287 The demand of substitute of Hindi language in davanagri script for Urdu in Persian script in colonial Punjab by urban Hindu community was not only cause the Hindu – Muslim communal conflict. But pro-Hindi campaign, Devanagri script form   Punjabi Hindu community    and   protec tive activities of Punjabi Muslim community for   Urdu language was pushed the both religious communities to protect and promote interest of their own communities.

Mastrubation Isnt It Harmful

Most Of the professionals in the field Of sexuality medicine claim that masturbation does not cause any harm to physical or mental health. Few even feel that masturbation is healthy, because it helps people to relive their sexual urge there by preventing unsafe sexual Quiet true, Masturbation may not cause any physical harm, if the standards of hygiene are maintained. UT the same cannot be true when we lock at it from a psychological perspective. Masturbation In one habit that can become a compulsive need in adolescents which Is carried Into adulthood, If necessary control is not brought about, at an appropriate time, by the person involved. The reasons being, It Is one pleasurable activity that can be done any time. The only requirement being some place with a little privacy.It also does not involve any identical expenditure or social curtailments. So there is an urge to experience the pleasure whenever there is privacy and opportunity. This habit In fact becomes a compulsive behavi or even at his stage because in every situation of privacy creates craving for masturbation. In the next stage they start looking for privacy whenever possible just for the sake of involving in masturbation, Most of the time â€Å"rest rooms† becomes the place that is used. Whenever they don't have any other place of privacy, Once this practice come existence the urge can becomes so compulsive that even when they have hectic schedules or important tasks to be completed, they may just take short breaks to restrooms to finish often urge, This stage indicates the obsessive psychological reoccupation With sexual thoughts and need for compulsive masturbation, to Overcome the thought. The other danger is the development of the belief that masturbation Is a stress buster. Yes masturbation can act as a diversion from stressful thoughts or events.It can very well act as a buffer. Taut this belief system can once again increase the frequency and preoccupation that many just use this es cape mechanism, and avoid exploring effective stress management methods. This can create limitations In their problem solving and decision making abilities The belief that masturbation can induce sleep also makes people involve in it every day before they go to bed and may a psychological cause of sleep disturbance, if they are in situations where they cannot involve in the habit before sleep the fantasies associated with the practice.Masturbation does not happen without the associated fantasies. When there is frequent involvement in masturbation, with in a short period, the normal fantasies lose its luster and become less stimulating. When the regular fantasies do not provide adequate arousal, it leads to suspicions ND worries, in some people, that they are losing their potency due to masturbatory habit. The bigger chunk of population shift to devising fantasies, which are pervert and deviant in nature to maintain the stimulation levels.The danger of these fantasies, is that when t hese people go through a real sexual experience, they don't find is so exciting or pleasurable, as what they have experienced in their wild fantasies. This can lead to dissatisfaction and lack of interest in real time sexual relationship and some times motivate the person to involve in deviant sexual acts. This can Jeopardize their marital relationship. In my experience I have come across many clients who tend to avoid sexual relationships and gain sexual satisfaction by involving in masturbatory practice even after marriage.The other threat to marital relationship from masturbatory habit is that, people who tend to involve in compulsive masturbation, try to reach the climax with in a very minimal time, which can lead to the development of premature ejaculation. Failure to get fully aroused in a real time situation, because of the fantasies, that have been ore stimulating can also lead to the development of performance anxiety.Also frequent masturbation, would create a status, where the person gets pleasure only by the self touch, to which he is habituated any may not be bale to feel the pleasure with the same intensity when their partner touch them during a sexual encounter which can also result in avoidance of real time sexual experience. The world of sexual fantasy is one place where the individual feel fully excited and satisfied. So there is all possibilities that they don't feel the necessity to mingle tit others or build relationships, because they are happy on their own in their own private world.This factor along with the compulsive thoughts to masturbate, which enforces the tendency to opt for isolation and places where their privacy is not infringed, so that they can involve in the act when ever they feel the need, becomes a barrier in developing social skills. Excessive masturbation can also lead to low self confidence and self esteem, which may be associated with the feelings of guilt associated with the habit or the pervert sexual fantasies, feel ings of lack of self intro, fear about health and immorality induced by religion and cultures and anxiety about their future marital life.The habit of masturbation can be treated as a totally harmless one. Preoccupation with the habit and related fantasies does have an impact on the productivity levels and the quality of life every person. So it is necessary that appropriate awareness is created, specifically among adolescents, platforms are provided to them for open minded discussion about their masturbatory practices