Dd-aa Assignment Example | Topics and Well Written Essays - 250 words

Dd-aa - Assignment Example The reverse movement in the above variables will result in a leftward shift. The AA curve illustrates the relationship between changes in the exogenous variable which is the Gross National Product as well as one of the endogenous variables known as the exchange rate located in the asset market model. The curve operates effectively as long as all the other exogenous variables are fixed. Factors that cause an upward shift in the AA curve include an increase in money supply, foreign interest rates and expected exchange rate. It may also be due to decline in the domestic price. Reverse changes in the above factors will lead to a downward shift in the AA curve (Friedman, 102-134). The DD-curve indicates a set of equilibrium in the Goods and Service market by describing the level of GNP at the prevailing exchange rate while the AA-curve shows a set of equilibrium in the asset market. A combination of the DD and AA curve will result in an equilibrium point at which the role played by both firms as well as households will influence a movement in the exchange rate and Gross Domestic Product level provided that other exogenous variables are fixed. Fiscal policy refer to the impact of government spending and taxation on macroeconomic conditions while monetary policy refers to the actions of the central bank that influences the supply of money in the

Liverpool one shopping development Essay Example for Free

Liverpool one shopping development Essay Liverpool’s CBD needed regeneration for a variety of reasons. During WW2, it was bombed heavily, due to it being a major port for resources from the USA. During the 1960s, it was rebuilt too quickly and then fell into disrepair before 2000, when the design and infrastructure was outdated. Many parts of the city, especially the CBD suffered from urban decline, with its population dropping by 50% and 45% of its industry also leaving. In addition, Liverpool faced competition for shopping by nearby Manchester and Chester, as well as out-of-town shopping centres like the Trafford Centre. Therefore, Liverpool’s CBD needed regeneration to be more attractive to consumers, and regain its spot in the top 5 shopping destinations in the UK. Liverpool One, the project to rejuvenate Liverpool’s CBD was completed in 2008. It was opened in phases on 29 May and 1 October 2008, with the final residential lots opening in early 2009. In the same year, Liverpool was named as the European Capital of Culture. Its total cost is approximately ? 1billion, with 42 acres of Liverpool city centre being redeveloped. It includes 3000 parking spaces, 169 stores or services, as well as a 5 acre park, and 500 new apartments. It also contains a 14-screen cinema and a 36-hole adventure golf centre. Shops present include Debenhams, John Lewis, Ted Baker, Waterstones, Starbucks, Topshop and Caffe Nero. These are all mainly comparison, high-order goods which are chain stores. The area is indoor, yet also mainly open-air. It is of a modern design, and is two storeys tall. There are many cafes and food areas, with many benches. There are also electronic maps and information panels across the centre. The pedestrian areas are wide and escalators are available to proceed to the higher floors. There have also been other improvements in the CBD, such as the rejuvenation of the Docks and the introduction of the Merseytram tram line in the CBD. As well as this, many roads and smaller streets in Liverpool have been rejuvenated and rebuilt as part of the redevelopments. Areas such as Princes Dock and the Kings Waterfront have seen heavy redevelopments. These have been to attract more tourists and shoppers to the CBD. The project has overall been successful as of yet, with 83% of consumers thinking that the city centre has improved. 91% of people said they were likely to return to Liverpool, and enjoyed the experience. And now, 40% of the shops in Liverpool One are new to the city, showing the popularity of the area. The previously redeveloped Albert Dock has been receiving an extra 100000 visitors per week, with Liverpool One itself receiving over 120000 visitors in the first day, and 13 million in the first year. It is safe the say the rejuvenation of Liverpool’s CBD has been a success, and that Liverpool One has played a big part in reversing the effect of urban decline.

Touch Interfaces Essay Example for Free

Touch Interfaces Essay Introduction Pointing at an object is the most basic human interaction, which is very important in human-machine interfaces. Similarly, creating gestures such as using ones hand and arm can provide information. For instance, pointing to a chair indicates asking for permission to sit down or pointing to indicate directions. The main goal of all the research done on touch interface and gesture recognition is to develop a system that can identify specific human gestures using human touch and use them to interact with Software application. Humans habitually use gesture to interact with other humans. Gestures can be used for everything such as pointing at an object for attention to conveying information about space and temporal characteristics [1]. Biologists define gesture, as the notion of gesture is to embrace all kinds of instances where an individual engages in movements whose communicative intent is paramount, manifest, and openly acknowledged [2]. Gestures that are related with speech are called gesticulation and gestures that are independent from speech are called autonomous gesture. Autonomous gestures have its own communicative language such as American Sign Language (ASL) as well as motion commands. There are many other types of gestures such as Semiotic – communicating meaning, Ergotic – manipulating objects and Epistemic – groping. There are six types of semiotic gestures and they are Symbolic (arbitrary), Deictic (pointing), Iconic (descriptive), Pantomimic (use of invisible objects), Beat (indicating flow of speech) and Cohesive (marker indicating related topics) [3]. Symbolic or Arbitrary gestures are gestures that can be learned but are not common in a culture setting and can be very useful because they can be specifically created for use of device control. An example is the set of gestures used for airport plane control. Deictic gestures are used to point at important objects and these gestures can be specific that refers to one object, in general that refers to class of object, or functions that symbolize intentions. An example is a simple hand gestures such as pointing to ones mouth when he or she is hungry. Related Technologies Today, there exist many image-based or device-based hardware techniques, which can be used as touch interface. For example, an image-based technique can detect gesture by capturing pictures of users hand motions gesture via camera. The captured image is then sent to Computer-vision software, which tracks the image and identifies the gesture. For instance, television sets that can be controlled by hand gesture instead of a remote control have been developed [4] [5] [6]. Basically, to turn the TV on, the user raises his open hand and the computer recognizes the gesture, which in return turns the TV on. Device-based techniques such as instrumented gloves, stylus and other position trackers have been developed, which recognize the movements and send the signals so that the system can understand the gesture. For example, Dexterous Handmaster [7] developed in 1987, initially used to control robot hand, which was very accurate but was not suitable for rapid movement. Power Glove [7] developed in 1989 by Mattel, which was resistive ink sensors for finger position, plus ultrasonic tracking and the Space Glove [7] developed in 1991, which was a plastic rings around fingers. Other gloves such as 5DT Data GloveTM [7], SuperGlove [7], Pinch Gloves [7] and CyberGlove [7]. However, the latest in computer technology is the G-Speak Gestural Technology System [8], a glove which is faster and easier to use compared to mouse and keyboard and using it one can move anything anywhere on the screen. At present, there exist many products, which are closely related with the hypothesis of this thesis. For example, the GyroPoint is a product of Gyration, Inc. in Saratoga, CA [9] [10]. The device can operate in two different modes. First, it can operate as a regular mouse and second, it can operate in the air (3D). Another example, the Bluewand, [11] which is a small pen-like device used to control Bluetooth enabled devices by hand-movements. Basically, a 6-axis accelerometer and gyroscope system detects devices full direction and movement in space. Bluewand can be used with verity of applications such as remote control for TV-set, cell-phone, MP3-player, etc. Overview of the Technology (Touch Interfaces) The ability to touch a computer screen and manipulate objects or control is a advance way of communication between human and computers and due to this advancement many types of touch system is developed such as point-of-sale systems, to information kiosks, to electronic whiteboards, iPod, iPhone etc. However, these systems have different ways of implementation in different applications. For example, using a desktop display for touch input as well as pen input, recognizing finger for touch on the screen. Other ways of implementation are such as Gesture recognition is a process through which a computer can recognize human gesture. Such interaction can make interface with computer more accessible and expressive for both the physically impaired and for young children who might find this type of interaction more natural. Gestures can be used in applications such as word processing, hand sign language, games, entertainment and educational approaches. There are other forms of gesture recognition than hand gestures. For example, finger pointing a way to select or move objects around, face tracking, eye motion and lip reading, etc. Technology that implements gestures has the ability to change the way humans interact with computers by eliminating input devices such as joysticks, mice and keyboards. Lots of conventional whole-hand input devices creates interface using non-contact methods or through some physical medium and such interfaces often needs contact of the hands and fingers with a hard, firm surface. As displays get larger, multi-user interaction is important as well as the ability to recognize two or more simultaneous inputs. As a result, wall-size touch displays became important for users as it enables to work with computer application and in the future human-body sized interfaces will become a natural way of interaction with the multiple users. Other related system is â€Å"A Camera-Based Touch Interface for Pervasive Displays† [13] developed by Gerald D. Morrison. Basically, the system contains smart camera in the corners of a 17-foot-wide wall display to determine the location of an object in front of, or in contact with, the display. The main object the user’s finger and the collected image are processed in such a way that it can recognize various attributes of the object’s, such as location relative to the display in three dimensional space. The information sent back to computer which generates the display, enabling touch control. Advantages of such system Many companies have established research centers all over the world to conduct research in developing new technologies. They emphasizes on managing its process in order to deliver product that are cheap and fast maintaining a good Information Management strategy. Manipulation of information using different applications and technologies became a potential information overload for many similar companies. Hence taking advantage of the new advance technologies to manage and maintain the information overload. Other advantages are such as having to interact with software application more closely compared t traditional ways of interactions. The term software was used in the early days of the software engineering field. It was used to describe how the rapid increase in computational power and the complexity of problems which now could be tackled. It refers to the difficulty of writing correct, understandable and variable computer programs. Having touch interface will help developer to interact with developing tools to developed advance software application. Today in the 21st century software is every where imaginable, when you check out at the grocery store, using a credit card, driving your car or listening to music in your new MP3 player just to name a few. Software development has undergone a change from its early days, the awareness of the software crisis has forced engineers to address the problems by various processes and methodologies and the industry are realizing that changing to more efficient ways of communicate with computers lead to better products with higher quality and reduced costs. However, there is always a problem that the tools and techniques invented today will need time to mature, to be introduced into industry.   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   The security implications of the system will be strong in order to assure safety for both the user and the system using finer print recognition. The main security issue such as data access must be implemented in such a way that the privilege given to the user is controlled and manipulated. Controlling the web-browsing habit such as browsing illegal or unwanted web sites need also to be controlled, hence providing user access to email, web sites using password and encryptions is essential. Keeping off the malicious users from accessing valuable company information and other external information that can be used against the company stuff and the company authorities needs to be taken under consideration. Sending emails and other attachments must be allowed according to hierarchy of access permissions. Other issues that need to be taken under consideration are such as the network password and security tokens needs to be changed constantly and most off all securing the connection to local devices that are connected to the network such as print servers and touch screen connected printers. Routers and switches should be organize and installed as securely as possible and web based configuration should be disabled as well as network access to the devices should be limited to the Grenada networks. To have a perfectly feasible operation and conduct the most proper ethical business functions is the first priority for most companies and businesses. The most critical issue related with IT is IT security where the objective is to take effective measures to decrease the threats exist today in IT related business such as e-commerce. Today, most companies prefer electronic information over traditional ways of storing and manipulation of information. Data are stored in huge database and process using different front-end software’s form anywhere in the world. IT security is made up of three main categories and they are Confidentiality, Integrity and Availability. Confidentiality is when company or an organization has sensitive information and does not want to disclose such information to anyone outside the company. Integrity is when companies want to update the system to adapt to future needs. As for availability, it is when a business implements a system it needs to make sure the system is up and running when needed. Threats such as customer’s information can be disclosed which can affect the credibility of any company; company’s information can be hacked by illegally, etc. There are many ways to improve the correct securities such as protecting data and information using different sophisticated firewall software, understanding threats and its impact in order to be protected forms it, calculating risk and deciding how to eradicate such risk. There are two basic ways to improve security and they are Bottom Up and Top Down. Bottom Up approach is not that precise but in order to implement such approach it is advisable to properly understand company policies, network topology and companies operating procedure. Top Down approach is methodical and more precise compared to Bottom Up approach but is slow and expensive. The main advantages of the touch interface are that it is centralized where it can access its information from using human touch. Therefore, if there are any security issues it can be dealt with using by tracking the finger-print. It is also flexible and scalable enough for new technologies to integrate with the system. Many flexible system and architecture can be designed so that it can be interoperable making all components work together in a synchronized fashion. This system can be used to backup critical information which is vital for both the system and the end-user. Conclusion As the information age advanced the need for computers became a daily part of human life. Computers have emerged from early abacus, papyrus and ENIAC to today’s main frame computer and super computers that can manipulate huge amount of information across the globe. The use of Touch screen was discovered by military in order to share information and after the first dial up connection; the use of touch screen became popular amongst local public. Today, computers are the most essential part of human life starting from basic calculators to storing and manipulating of terabits of information. Use of Touch screen is mostly possible if one uses computers or other devices such as mobiles. Need for speedy information has become an important issue in today’s business. Using such devices Touch screen caused a revolution in our society. Peoples shopping style is also changing because of Touch screen. Selling products over the touch screen is cheap, fast and easy for both the company and the customer. Hence issues such as privacy and ethics are most important and needs to be concentrated on by the governments and education institute. Many of the ethical issues involve privacy. For example, privacy concerning e-mail uses by the employees, head office of a company and individuals. System such as malleable surface interface [12] can be used in applications that require physically touching the screen and its objects performed by the human hands or finger, such as sculpting and massage. Even though, many touch technology systems are suitable for small displays such as iPod, iPhone, the system can be also used in big screen such TV, or directly interacting with the pc monitor. This way of communication is very attractive because they are more versatile than other input devices as well as can be made inexpensively. While touch sensing is very common but having multi user interaction has become more essential. Having to interact with a system with more than one finger at a time useful for larger interaction scenarios such as interactive walls and tabletops. Many researchers experimenting with a wide variety of application scenarios and communication modalities that utilize multi-touch input. It is a rich area for research, and has potential for advances in efficiency, usability, and intuitiveness of the future UI designed. Today there exist mobiles with touch screen and stroke interfaces as compared to those with button, thumbwheel, trackballs, and stylus etc interfaces. The traditional ways of interaction for example using buttons, and cognitively arbitrated by the need to roll a wheel to scroll the cursor focus kept us distance with the technology invented. Hence, to touch something would be to minimize the distance between human and the computer. Using gesture similar to Nintendo Wii, is a breakthrough in advancement of GUI. Other devices such as LG Prada, HTC phone and Apple iPhone help us to use our fingers to feel the system rather just using the system. The touch system is already been used in wireless devices successfully. Wireless communications offer organizations and users many benefits such as portability, flexibility and lower installation costs. Wireless technologies cover a broad range of capabilities toward different uses and needs. Wireless local area network (WLAN) devices, for instance, allow users to move their laptops from place to place within their offices and homes without the need for wires and without losing network connectivity. However, risks are natural in any wireless technology. The most significant source of risks in wireless networks is that the technology’s underlying communications medium such as the airwave, is open to intruders. Having touch screen developers and interact and develop application using advance GUI’s. Today, touch screen technology is used everywhere to cut down cost as well as speed up the development process by keeping the quality of the application insured. Touch screen based development helps to build software applications by connecting multiple components together which are produced independently. In order for this communication to take place we must have an interface between the components in such a way that is helps to develop the overall application as well as implementing it in the future applications. However, it is the compatibility between connected component interfaces that determines the success of the implementation of the components. To be precise, an interface is made of number of operations which can be manipulated by the user. The operations play a vast role in implementing the interface and use of the interface by the client or the user. Today, Internet is a good way of doing business and use of internet is constantly increasing. Improving the GUI and converting to touch screen will become very important in the future for the use of World Wide Web because it helps to communicate globally and deliver products to customers who can not purchase the products. It also helps to increases advertising and by providing one to one marketing. E-commerce is a very easy way of gathering information form its customers or potential customers. One of the biggest advantages of using the internet is its efficient ways of reducing warehousing and inventory. A Company needs a network that provides fast and efficient way to manipulate its information. Compared to its traditional manual filing system accessing, touch screen will provide information with speed, accuracy, and accessibility. A sophisticated design of the system will allow access from anywhere in the world which helps to manipulate and send information through the world. Hence, the touch screen is reliable in assuring speed, data reliability, cheap and strong security. However, it is extremely reliable and main important thing is that no extra input device is needed. Touch screen gives fast and superior performance which is sufficient for file sharing, gaming, and high-speed access. As for security, touch screen will have software application that recognizes finger print. Traditional GUI and access can be three or four times expensive compared to touch screen. A both traditional ways and touch screen can be a good option for any company depending on the difficulty of accessing the information the company. However, touch screen is easier to install, more reliable and mobility is excellent where as traditional is more difficult to install with limited mobility. Reference [1].  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   A Brief Overview of Gesture Recognition by Charles Cohen. http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/COHEN/gesture_overview.html ; Accessed 7th, Nov, 2007 [2]   Ã‚  Ã‚  Ã‚  Ã‚   Jean-Luc Nespoulous, Paul Perron, and Andre Roch Lecours. The Biological Foundations of Gestures: Motor and Semiotic Aspects. Lawrence Erlbaum Associates, Hillsdale, MJ, 1986. http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/COHEN/gesture_overview.html; Accessed 7th, Nov, 2007 [3].   Ã‚  Ã‚  Ã‚   GESTURE BASED INTERACTION; Steven Damer; http://www-users.itlabs.umn.edu/classes/Fall-2004/csci8980-1/slides/gesture.pdf; Accessed 7th, Nov, 2007 [4]   Ã‚  Ã‚  Ã‚  Ã‚   Computer Vision for Computer Interaction SIGGRAPH Computer Graphics magazine, November 1999 W. T. Freeman, P. A. Beardsley, H. Kage, K. Tanaka, K. Kyuma, C. D. Weissman. Also available as MERL-TR99-36. [5]  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   Computer Vision for Interactive Computer Graphics; IEEE Computer Graphics and Applications, Vol. 18, No. 3, May-June 1998; W. T. Freeman, D. B. Anderson, P. A. Beardsley, C. N. Dodge, M. Roth, C. D. Weissman, W. S. Yerazunis, H. Kage, K. Kyuma, Y. Miyake, and K. Tanaka. Also available as MERL-TR99-02. [6]  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   Computer Vision for Computer Games In 2nd International Conference on Automatic Face and Gesture Recognition, Killington, VT, USA. IEEE. W. T. Freeman, K. Tanaka, J. Ohta, K. Kyuma . Also available as MERL-TR96-35. [7]  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   Gesture Based Interaction; Steven Damer; http://www-users.itlabs.umn.edu/classes/Fall-2004/csci8980-1/slides/gesture.pdf; Accessed 7th, Nov, 2007 [8]  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   Gesture Glove Not Science Fiction;   LOS ANGLEES, Aug. 23, 2005; http://www.cbsnews.com/stories/2005/08/23/eveningnews/main792311.shtml; Accessed 7th, Nov, 2007 [9]  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   An Evaluation of Two Input Devices for Remote Pointing; Scott MacKenzie and Shaidah Jusoh; http://www.yorku.ca/mack/ehci2001.pdf ; Accessed 7th, Nov, 2007 [10]  Ã‚  Ã‚  Ã‚   Gyration, Inc., Saratoga, California. http://www.gyration.com/ ; Accessed 7th, Nov, 2007 [11]  Ã‚  Ã‚  Ã‚  Ã‚   Bluewand. A versatile remote control and pointing device; Thomas Fuhrmann , Markus Klein, and Manuel Odendahl; http://i30www.ira.uka.de/research/documents/p2p/2003/fuhrmann03bluewand-KiVS.pdf ; Accessed 7th, Nov, 2007 [12]  Ã‚  Ã‚  Ã‚  Ã‚   Florian Vogt, Timothy Chen, Reynald Hoskinson, Sidney Fels; A Malleable Surface Touch Interface; Human Communication Technologies Laboratory; The University of British Columbia; http://hct.ece.ubc.ca/publications/pdf/vogt-chen-hoskinsin-fels-SIGGRAPH2004.pdf; Accessed 7th, Nov, 2007 [13]  Ã‚  Ã‚  Ã‚  Ã‚   Gerald D. Morrison; A Camera-Based Touch Interface for Pervasive Displays; SMART Technologies Inc., 1207 – 11 Ave. SW, Suite 300, Calgary, AB, Canada T3C 0M5; http://ubicomp.algoritmi.uminho.pt/perdisplay/docs/Morrison-Camera%20Touch_SV_Rev1.pdf; Accessed 7th, Nov, 2007;

Importance Of Time In Distributed Systems

Importance Of Time In Distributed Systems Time is an important and interesting issue in Distributed Systems for several reasons. First, time is a quantity we always want to measure accurately. In order to know at what time of day a particular event occurred at a particular computer, it is necessary to synchronize its clock with an authoritative, external source of time. Second, algorithms that depend upon clock synchronization have been developed for several problems in distribution; these include maintaining the consistency of distributed data, checking the authenticity of a request sent to a server and eliminating the processing of duplicate updates [1] In Centralized systems, there is no need for clock synchronization because, generally, there is only a single clock. A process gets the time by simply issuing a system call to the kernel. When another process after that tries to get the time, it will get a higher time value. Thus, in such systems, there is a clear ordering of events and there is no ambiguity about the times at which these events occur. [4] In Distributed systems, there is no global clock or common memory. Each processor has its own internal clock and its own notion of time. In practice, these clocks can easily drift apart by several seconds per day, accumulating significant errors over time. Also, because different clocks tick at different rates, they may not remain always synchronized although they might be synchronized when they start. This clearly poses serious problems to applications that depend on a synchronized notion of time. Distributed systems are subject to timing uncertainties as certain processes may lack a common notion of real time. Due to an uncertainty in message delay time, absolute process synchronization is known to be impossible for such systems The literature presents issues of timing in distributed systems, physical clocks and their synchronization problems, algorithms for synchronizing physical clocks are presented with their limitations, and also techniques for implementing logical clocks which are used to monitor the order of events without measuring the physical time at which the events occurred The concept of time Let us begin by asking this simple question; does anybody really know what time it is [3] As Lamport notes, the concept of time is fundamental to our way of thinking [7] In fact, real time helps to master many problems of our decentralized real world. Time is also a useful concept when considering possible causality. Consider a person suspected of a crime, if that person has an alibi because he or she was far enough away from the site of the crime at some instant close enough to the time of the crime, then he or she cannot be the culprit. Timing problems Accurate time is important to determining the order in which events occur; [3] this is a basic standard of transactional integrity, system and networkà ¢Ã¢â€š ¬Ã‚ wide logging, auditing, troubleshooting and forensics. Having an accurate time source plays a critical role in tracing and debugging problems that occur on different platforms across a network. Events must be correlated with each other regardless of where they were generated. Furthermore, the notion of time (or time ranges) is used in many forms of access control, authentication, and encryption. In some cases, these controls can be bypassed or rendered inoperative if the time source could be manipulated. For example, a payroll function could be tricked into providing access over a weekend when normally it would be restricted to normal business hours. [3] Physical clocks Most computers today keep track of the passage of time with a battery-backed up Complementary Metal Oxide Semiconductor (CMOS) clock circuit, driven by a quartz resonator. This allows the timekeeping to take place even if the machine is powered off. When on, an operating system will generally program a timer circuit (a Programmable Interval Timer, or PIT, in older Intel architectures and Advanced Programmable Interrupt Controller, or APIC, in newer systems.) to generate an interrupt periodically (common times are 60 or 100 times per second). The interrupt service procedure simply adds one to a counter in memory. While the best quartz resonators can achieve an accuracy of one second in 10 years, they are sensitive to changes in temperature and acceleration and their resonating frequency can change as they age. Standard resonators are accurate to 6 parts per million at 31 °C, which corresponds to  ±Ãƒâ€šÃ‚ ½ second per day. The problem with maintaining a concept of time is when multiple entities expect each other to have the same idea of what the time is. Two watches hardly ever agree. Computers have the same problem: a quartz crystal on one computer will oscillate at a slightly different frequency than on another computer, causing the clocks to tick at different rates. The phenomenon of clocks ticking at different rates, creating an ever widening gap in perceived time is known as clock drift. The difference between two clocks at any point in time is called clock skew and is due to both clock drift and the possibility that the clocks may have been set differently on different machines. The Figure below illustrates this phenomenon with two clocks, A and B, where clock B runs slightly faster than clock A by approximately two seconds per hour. This is the clock drift of B relative to A. At one point in time (five seconds past five oclock according to As clock), the difference in time between the two clocks is approximately four seconds. This is the clock skew at that particular time. Compensating for drift We can envision clock drift graphically by considering true Coordinated Universal Time (UTC) flowing on the x-axis and the corresponding computers clock reading on the y-axis. A perfectly accurate clock will exhibit a slope of one. A faster clock will create a slope greater than unity while a slower clock will create a slope less than unity. Suppose that we have a means of obtaining the true time. One easy (and frequently adopted) solution is to simply update the system time to the true time. To complicate matters, one constraint that well impose is that its not a good idea to set the clock back. The illusion of time moving backwards can confuse message ordering and software development environments. If a clock is fast, it simply has to be made to run slower until it synchronizes. If a clock is slow, the same method can be applied and the clock can be made to run faster until it synchronizes. The operating system can do this by changing the rate at which it requests interrupts. For example, suppose the system requests an interrupt every 17 milliseconds (pseudo-milliseconds, really the computers idea of what a millisecond is) and the clock runs a bit too slowly. The system can request interrupts at a faster rate, say every 16 or 15 milliseconds, until the clock catches up. This adjustment changes the slope of the system time and is known as a linear compensating Function. After the synchronization period is reached, one can choose to resynchronize periodically and/or keep track of these adjustments and apply them continually to get a better running clock. This is analogous to noticing that your watch loses a minute every two months and making a mental note to adjust the clock by that amount every two months (except the system does it continually). Synchronizing physical clocks With physical clocks, our interest is not in advancing them just to ensure proper message ordering, but to have the system clock keep good time. We looked at methods for adjusting the clock to compensate for skew and drift, but it is essential that we get the time first so that we would know what to adjust. One possibility is to attach a GPS (Global Positioning System) receiver to each computer. A GPS receiver will provide time within  ± 1 msec. of UTC time but Unfortunately, they rarely work indoors. Alternatively, if the machine is in the U.S., one can attach a WWV radio receiver to obtain time broadcasts from Texas, Colorado or Washington, DC, giving accuracies of  ± 3-10 msec. depending on the distance from the source. Another option is to obtain a GOES (Geostationary Operational Environment Satellites) receiver, which will provide time within  ± 0.1 msec. of UTC time. For reasons of economy, convenience, and reception, these are not practical solutions for every machine. Most machines will set their time by asking another machine for the time (preferably one with one of the aforementioned time sources). A machine that provides this information is called a time server. Several algorithms have been proposed for synchronizing clocks and they all have the same underlying model of the system Cristians algorithm The simplest algorithm for setting the time would be to simply issue a remote procedure call to a time server and obtain the time. That does not account for the network and processing delay. We can attempt to compensate for this by measuring the time (in local system time) at which the request is sent (T0) and the time at which the response is received (T1). Our best guess at the network delay in each direction is to assume that the delays to and from are symmetric (we have no reason to believe otherwise). The estimated overhead due to the network delay is then (T1- T0)/2. The new time can be set to the time returned by the server plus the time that elapsed since the server generated the timestamp: Suppose that we know the smallest time interval that it could take for a message to be sent between a client and server (either direction). Lets call this time Tmin. This is the time when the network and CPUs are completely unloaded. Knowing this value allows us to place bounds on the accuracy of the result obtained from the server. If we sent a request to the server at time T0, then the earliest time stamp that the server could generate the timestamp is T0 + Tmin. The latest time that the server could generate the timestamp is T1 Tmin, where we assume it took only the minimum time, Tmin, to get the response. The range of these times is: T1 T0 2Tmin, so the accuracy of the result is: Errors are cumulative. If machine A synchronizes from a server B and gets an accuracy of  ±5 msec but server B in turn got its time from server C with an accuracy of  ±7 msec, the net accuracy at machine A is  ±(5+7), or  ±12 msec. Several time requests may be issued consecutively in the hope that one of the requests may be delivered faster than the others (e.g., it may be submitted during a time window when network activity is minimal). This can achieve improved accuracy. Cristians algorithm suffers from the problem that afflicts all single-server algorithms: the server might fail and clock synchronization will be unavailable. It is also subject to malicious interference. Berkeley algorithm The Berkeley algorithm, developed by Gusella and Zatti in 1989 [8], is form of an internal synchronization that does not assume that any machine has an accurate time source with which to synchronize. Instead, it opts for obtaining an average time from the participating computers and synchronizing all machines to that average. The machines involved in the synchronization each run a time dà ¦mon process that is responsible for implementing the protocol. One of these machines is elected (or designated) to be the master. The others are slaves. The server polls each machine periodically, asking it for the time. The time at each machine may be estimated by using Cristians method to account for network delays. When all the results are in, the master computes the average time (including its own time in the calculation). The hope is that the average cancels out the individual clocks tendencies to run fast or slow. Instead of sending the updated time back to the slaves, which would introduce further uncertainty due to network delays, it sends each machine the offset by which its clock needs adjustment. The operation of this algorithm is illustrated in the Figure below. Three machines have times of 3:00, 3:25, and 2:50. The machine with the time of 3:00 is the server (master). It sends out a synchronization query to the other machines in the group. Each of these machines sends a timestamp as a response to the query. The server now averages the three timestamps: the two it received and its own, computing (3:00+3:25+2:50)/3 = 3:05. Now it sends an offset to each machine so that the machines time will be synchronized to the average once the offset is applied. The machine with a time of 3:25 gets sent an offset of -0:20 and the machine with a time of 2:50 gets an offset of +0:15. The server has to adjust its own time by +0:05. The algorithm also has provisions to ignore readings from clocks whose skew is too great. The master may compute a fault-tolerant average averaging values from machines whose clocks have not drifted by more than a certain amount. If the master machine fails, any other slave could be elected to take over Logical clocks Lets again consider cases that involve assigning sequence numbers (timestamps) to events upon which all cooperating processes can agree. What matters in these cases is not the time of day at which the event occurred but that all processes can agree on the order in which related events occur. Our interest is in getting event sequence numbers that make sense system-wide. If we can do this across all events in the system, we have something called total ordering: every event is assigned a unique timestamp (number), every such timestamp is unique. However, we dont always need total ordering. If processes do not interact then we dont care when their events occur. If we only care about assigning timestamps to related (causal) events then we have something known as partial ordering. Leslie Lamport [7] developed a happened before notation to express the relationship between events: aà ¢Ã¢â‚¬  Ã¢â‚¬â„¢b means that a happened before b. If a represents the timestamp of a message sent and b is the timestamp of that message being received, then aà ¢Ã¢â‚¬  Ã¢â‚¬â„¢b must be true; a message cannot be received before it is sent. This relationship is transitive. If aà ¢Ã¢â‚¬  Ã¢â‚¬â„¢b and bà ¢Ã¢â‚¬  Ã¢â‚¬â„¢c then aà ¢Ã¢â‚¬  Ã¢â‚¬â„¢c. If a and b are events that take place in the same process the aà ¢Ã¢â‚¬  Ã¢â‚¬â„¢b is true if a occurs before b. The importance of measuring logical time is in assigning a time value to each event such that everyone will agree on the final order of events. That is, if aà ¢Ã¢â‚¬  Ã¢â‚¬â„¢b then clock (a) < clock (b) since the clock (our timestamp generator) must never run backwards. If a and b occur on different Processes that do not exchange messages (even through third parties) then aà ¢Ã¢â‚¬  Ã¢â‚¬â„¢b is not true, these events are said to be concurrent: there is no way that a could have influenced b. Each event is assigned a timestamp by its respective process. The process simply maintains a global counter that is incremented before each event gets a timestamp. If we examine the timestamps from our global perspective, we can observe a number of peculiarities. Event g, the event representing the receipt of the message sent by event a, has the exact same timestamp as event a when it clearly had to take place after event a. Event e has an earlier time stamp (1) than the event that sent the message (b, with a timestamp of 2). Lamports algorithm Lamport [7] proposed an algorithm that forces the resequencing of timestamps to ensure that the happened before relationship is properly depicted for events related to sending and receiving messages. It works as follows: Each process has a clock, which can be a simple counter that is incremented for each event. The sending of a message is an event and each message carries with it a timestamp obtained from the current value of the clock at that process (sequence number). The arrival of a message at a process is also an event will also receive a timestamp by the receiving process, of course. The process clock is incremented prior to time stamping the event, as it would be for any other event. If the clock value is less than the timestamp in the received message, the systems clock is adjusted to the (messages timestamp + 1). Otherwise nothing is done. The event is now time stamped. If we apply this algorithm to the same sequence of messages, we can see that proper message ordering among causally related events is now preserved. Note that between every two events, the clock must tick at least once. [4] Lamports algorithm [7] allows us to maintain proper time ordering among causally- related events. In summary, Lamports algorithm requires a monotonically increasing software counter for a clock that has to be incremented at least when events that need to be time stamped take place. These events will have the clock value, or Lamport timestamp, associated with them. For any two events, where aà ¢Ã¢â‚¬  Ã¢â‚¬â„¢b, L (a) < L (b) where L(x) represents the Lamport timestamp for event x. Lamport timestamps [7] assure us that if there is a causal relationship between two events, then the earlier event will have a smaller time stamp than the later event. Causality is achieved by successive events on one process or by the sending and receipt of messages on different processes. As defined by the happened-before relationship, causality is transitive. For instance, events a and f are causally related in the figure above (through the sequence a, b, e, f). Implementing Logical clocks To implement logical clocks, [11] each process p, maintains data structures that give it the following two capabilities: A logical clock, denoted by C, that helps P, measure its own progress; and A global logical clock denoted by gC, that represents Ps local view of the global logical time. A protocol is presented to update the data structures; the protocol ensures that a processs logical clock and its view of the global time are consistent. The protocol consists of the following two rules: R1. maintains how a process updates the local logical clock when it executes an Event, whether send or receive R2. maintains how a process updates its global logical clock to update its view of the Global time. It dictates what information about the logical time a process Piggybacks in a message and how the receiving process uses this information to Update its view of the global time A distributed system consisting of logical clocks differ in their representation of logical time and in the protocol for updating logical clocks. However, all systems consisting of logical clocks implements some form of R1 and R2 and thereby achieving the fundamental monotonicity property associated with events and casualty Total ordering of events Note that it is very possible for multiple non-causal (concurrent) events to share identical Lamport timestamps (e.g., c, e, and h in the Figure above). This may cause confusion if multiple processes need to make a decision based on the timestamps of two events. The selection of a specific event may not matter if the events are concurrent but we want all the processes to be able to make the same decision. This is difficult if the timestamps are identical. Fortunately, theres an easy remedy. We can create a total order on events by further qualifying them with identities of processes. We define a global logical timestamp (Ti,i) where Ti represents the local Lamport timestamp and i represents the process ID (in some globally unique way: for example, a concatenation of host address and process ID). We are then able to globally compare these timestamps and conclude that There is no physical significance to the order since process identifiers can be arbitrary and do not relate to event ordering but the ability to ensure that no two Lamport timestamps are the same globally is helpful in algorithms that need to compare these timestamps. In real life, depending on the application, one may use a combination of thread ID, process ID, and IP address as a qualifier to the timestamp. Vector clocks If two events are causally related and event e happened before event e then we know that L (e) < L (e). However, the converse is not necessarily true. With Lamports algorithm, if L (e) < L (e) we cannot conclude that eà ¢Ã¢â‚¬  Ã¢â‚¬â„¢e. Hence, if we look at Lamport timestamps, we cannot conclude which pairs of events are causally related and which are not. One solution that has been proposed to deal with this problem is the concept of vector clocks (proposed by Mattern in 1989 and Fidge in 1991) [9, 10]. A vector clock in a system of N processes is a vector of N integers. Each process maintains its own vector clock (Vi for a process Pi) to timestamp local events. Like Lamport timestamps, vector timestamps (the vector of N integers) are sent with each message. The rules for using vector clocks are: The vector is initialized to 0 at all processes: Vi[j] = 0 for i,j = 1, à ¢Ã¢â€š ¬Ã‚ ¦, N Before a process Pi timestamps an event, it increments its element of the vector in its local vector: Vi[i] = Vi[i]+1 A message is sent from process Pi with Vi attached to the message. When a process Pj receives a vector timestamp t, it compares the two vectors element by element, setting its local vector clock to the higher of the two values: Vj[i] = max(Vj[i], t[i]) for i=1, à ¢Ã¢â€š ¬Ã‚ ¦, N We compare two vector timestamps by defining: V = V iff V[j] = V'[j] for i=1, à ¢Ã¢â€š ¬Ã‚ ¦, N V à ¢Ã¢â‚¬ °Ã‚ ¤ V iff V[j] à ¢Ã¢â‚¬ °Ã‚ ¤ V'[j] for i=1, à ¢Ã¢â€š ¬Ã‚ ¦, N For any two events e, e, if eà ¢Ã¢â‚¬  Ã¢â‚¬â„¢e then V(e) < V(e). This is the same as we get from Lamports algorithm. With vector clocks, we now have the additional knowledge that if V(e)

brave new world :: essays research papers

Brave New World: Draft   Ã‚  Ã‚  Ã‚  Ã‚  Huxley's: Brave New World takes into consideration so much of what really goes on in the world now. From the separation of the sexes to the, still in progress, cloning of the new millenium.   Ã‚  Ã‚  Ã‚  Ã‚  Today regardless of all the women's rights acts and laws against discrimination due to race or sex, women still seem inferior in some ways. There are still housewives, while not as many as there were say fifty years ago, as well as women still found stuck in the kitchen cooking dinner for the husband as oppose to the husband taking hold of the kitchen and other household duties. Women, more commonly years ago, are often time s thought of as nothing more than a way to make a baby. In older times women were nothing, but the mere way of bearing a child. While male condoms are widely available and used, it is often times the responsibility of the woman to keep up with other birth control methods such as birth control, Depo-Provera shots, abortions and other forms of birth control.   Ã‚  Ã‚  Ã‚  Ã‚  From a political standpoint, there has yet to be a female president in the United States of America. In fact male politicians out weigh the number of female politicians hands down. There are only males in charge of everything throughout Brave New World. All of the power is left to men to distribute. In fact, most directors or supervisors of big, major companies and firms are usually male. Not that a woman couldn't perform the same duties just as efficiently, women are just more commonly found lower down the working scale. In addition to the majority of higher positioned workers being men, there are a number of cases where men and women may perform equal jobs, yet the men still earn a higher salary.   Ã‚  Ã‚  Ã‚  Ã‚  Another stretch of the world we live in today is the explicit use of drugs. In America there are a ridiculously high number of people who use or abuse drugs. I compared a commonly used drug such as ecstasy, shrooms or even alcohol to the very frequently used drug, soma that was used in Brave New World. Alcoholics who drink a lot here in the United States sometimes beat their wives (husbands), children or drive drunk. Sometimes people simply drink socially, such as many college students are known to do, but still get a false since of happiness that exists only while they are drunk.

Does TV Affect American Culture Essay -- essays research papers

Does Television Shows Reflect American Culture? There are many movies and television shows that reflect American culture. A show or movie must address some current societal problem or trend in order to truly reflect American life; murder, rape, racism, and, on a less serious note, parties, shopping, and sports are topics that deserve serious consideration by the public and the media. The show Beverly Hills 90210 attempts to be an accurate portrayal of the life of a typical well-off American teenager growing up in the 80's and 90's. The producers of the show attempt to integrate many real life situations in to the show. By doing this they are suggesting to the audience, which happens to be geared toward teenagers and young adults, that what the characters do in the show is the ideal way to deal with these types of situations. Many aspects of American culture are represented on the television show Beverly Hills 90210, or just 90210 as it is commonly referred to. During the first year or so of Beverly Hills 90210 it dealt with the su bject of murder/homicide. One of David's best friends was playing with a gun that he had acquired during a summer vacation to the mid-West. The friend shot himself by accident; what followed was a time of mourning for David and a recollection of many fond memories of the times they shared together. This episode's tragedy brought the characters in the show closer together. Many innocent children, and sometimes adults, are killed accidentally playing with guns, or by drive-by shootings. This is a major problem in the United States and the show is trying to get the message out that it is not a safe thing to do. It also raises the question as to why access of guns is so readily available to anyone. Every night on the news, someone can see many incidents in which there are suffering resulting from guns. Furthermore, the availability of guns makes the public scared. Children have images of adults using guns for hunting or game. In the adolescents' mind it appears that guns are not a bad i tem to own, when in reality guns are extremely dangerous weapons. Beverly Hills 90210 makes a strong attempt to impress upon its viewers that these accidents can be precautions. The show sends a message to the younger generation, which are becoming more and more violent, to stay away from things that result in violence like... ...s right in with the materialistic values promoted by our society in print, in television, in commercials, in movies - in other words, in all aspects of the media. All economic echelons of society in the United States are encouraged to purchase name brand clothing and other apparel. The"American Dream" of shopping and credit cards is a reality in the show. The setting of the show is Beverly Hills, California, the home of all the popular trends and famous stars. This location, along with rich parents, provides for the perfect situation to make them look like rich brats. Although Beverly Hills 90210 is not a perfect reflection of American culture, it does lend itself to the stereotype of having a huge wardrobe and living the "American Dream". In the ten years during which 90210 has been on the air, the show has dealt with many topics. From the Persian Gulf War and high school, to AIDS and the Internet, the show has reflected many aspects of American culture. Beve rly Hills 90210 sends a message to the viewers to make the best of one's life. Hopefully many of the viewers will be able to attain the "American Dream" that is the essence of American culture.

Karl Marx :: essays research papers fc

Karl Marx The most influential person pre-1900   Ã‚  Ã‚  Ã‚  Ã‚  Ã¢â‚¬Å"If a fair list were given, †¦, it would seem reasonable to say that he was bad tempered, caustic, fierce, vain, self-sacrificing, selfish, whining, capable of great love, a good father, a lover of mankind, fatherly to all, honest, scrupulous, tender, brilliant, eminently rational, racist in an off hand manner, irony as an art, a person obsessed with irony, obsessive in general, flexible, a brilliant politician, but a candid one as they go.†(Olson 11) Hopefully we have all heard the name Karl Marx at some time or another, but what did he do that’s so important? Marx was a great influence from before 1900, but his influences are also felt throughout this century. Marx was the most influential person in world history before 1900 because he developed a new form of government, Marxism influenced several world leaders, and Marxism can be linked to such important events as the Russian Revolution and the Cold War.   Ã‚  Ã‚  Ã‚  Ã‚     Ã‚  Ã‚  Ã‚  Ã‚  The main reason Marx is so important is because of the political philosophy that he developed, appropriately dubbed Marxism and commonly called Communism. Marx’s goal was to spiritually release mankind by freeing him of his economic chains and allowing him to find harmony with his fellow man and with nature (Fromm 3). Marx’s interests in economics started when he wrote two extensive essays on the position of Eifel peasants and Moselle vinegrowers (Leonhard 4). His interests were also engaged by the labor movement, which the effects of were just becoming apparent (Leonhard 4). As talk about communist ideas first began to rise, Marx was reserved about his opinions (Leonhard 4). In spite of his reservations, Marx heavily researched the contemporary French literature on socialism and Communism, and in 1843 moved to Paris, the heart of the revolutionary movement (Leonhard 4). While in Paris, one of the most important events of his stay occurred, his meeti ng with Friedrich Engels. â€Å"This was the beginning of a lifelong friendship and collaboration of the founders of scientific socialism.† (Leonhard 5) Marx and Engels emphasized the connection of socialist aims, economic reality, and the struggle of the working class (Leonhard 5-6). In 1847 Marx was invited to join the â€Å"League of the Just† which was later renamed the â€Å"Communist League†(Leonhard 6). Marx and Engels were instructed to work out a political program form the Communist League (Leonhard 6-7). Engels sketched a draft of questions and answers know as the Principles of Communism, after reworking by Marx this became the Communist manifesto (Leonhard 7).