Lecture 2 (August 19, 2015)
Lecture 2 (August 19, 2015) EE8086
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This 17 page Class Notes was uploaded by Andreas on Thursday September 10, 2015. The Class Notes belongs to EE8086 at Nanyang Technological University taught by Lee-Tay, Annie; Poenar Daniel Puiu; Yong Ken Tye; in Summer 2015. Since its upload, it has received 132 views. For similar materials see Astronomy - Stars, Galaxies And Cosmology in Electrical Engineering at Nanyang Technological University.
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Date Created: 09/10/15
Ancient Astronomy Almost every ancient civilization exercised astronomy 0 Producing impressive structures that aid them in observation 0 Use it for various things gt track and predict seasons calendar eclipses lunar cycles planets and stars daily timekeeping navigation predict eclipses Origin of modern astronomy gt started when telescope was invented there are huge advances in knowledge Egyptian obelisk 3150 BC 31BC Tall foursided monument with pyramidlike shape at the top 0 Shadow produced act like hourhand of the clock 0 Divide daytime into 12 equal parts origin for modern clock system 0 At night time is estimated from position and phase of Moon gt less accurate Stonehenge Southern England 2750 BC 1550 BC 0 One of the oldest still standing structures for season marking gt the building process is still mysterious o For season tracking gathering place social religious Aubrey holes are probably used to predict eclipse 0 Longterm use might be for burial gt 240 buried there mostly in Aubrey holes Templo Mayor Aztec civilization Mexico 1325 AD 1521 AD 0 Twin temples at the top of flattopped pyramid When it is equinox the sun will rise in between the temple 0 1 temple refer to their god of war the other to god of food and agriculture Sun Dagger ancient Anasazi New Mexico US 1200 BC 1300 AD 0 19turn spiral carved on cliff wall 0 Sun s ray forms a dagger of sunlight at the center only at the noon of summer solstice The dagger shift to the leftright on equinoxes o On winter solstice the dagger split into 2 Mayan observatory Chichen Itza Mexico 200 AD 900 AD 0 Windows at top level now partly destroyed act as observation spot gt position of sunrise sunset motion of Moon and Venus Experts in predicting eclipses gt mostly based on calculation Earliest record of Supernova in the form of bone or tortoise shell inscription at 1400 BC Star map from Tang Dynasty 700 AD displaying Ursa Major Sagittarius Capricornus Ancient Greek Science Modern science originated from most ancient Mediterranean civilization ultimately ancient Greece 0 Rose in Middle East in 800 BC was well established in 3 century time gt good leader prosper nation 0 Place for all kinds of ideas and culture to meet gt high trading activity increase weapons and medicines development 0 Ideas spread by Alexander the Great 356323 BC who had high interest in science encourage by his teacher Aristotle on nation that he conquered Library of Alexandria opened 300 BC after he died gt world s most important research center for N700 years destructed and burned down by 4 major wars reducing our advancement by 10 years gt a few scripts were kept at Smithsonian museum Greek s science principles are still used in modern science gt first people to make models of nature 0 Explain patterns in nature without referring to their myth beliefs etc Explanation is wrong if it disagreed with observed facts At bronze and iron age people believe that the Earth is flat So they start to explore the Earth by sea to prove the belief Idea of round Earth was originated from Pythagoras 500 BC Early Greek philosophers Plato Aristotle etc believed on geocentric model of universe 0 Earth is the center of a perfectly spherical universe with planets and stars orbiting around it 0 Heaven universe must be perfect gt object must move on the sphere or in perfect circles 0 Hard to explain the apparent retrograde motion of planets objects appear to be moving backwards or in reverse at some point and stellar parallax difference in direction of a celestial object as seen by an observer from two widely separated points 0 Solved easily by heliocentric model gt Aristarchus 260 BC 0 Didn t have much support since it contradicted the common idea of physics at the time o Greeks came up with some ideas trying to cover the flaws which are refined for centuries and widely adopted o Ptolemaic model gt each planet moved on small circle whose center around Earth on a large circle epicycles Copernican Revolution Ptolemaic model is mathematically complex gt as time goes on the model tries to predict other events creating even more flaws Copernicus used heliocentric model and figured a mathematically simpler model At that time Ptolemaic model was getting more and more inaccurate His work published on the day he died May 24 1543 fundamentally changed our perception of universe Heliocentric model Sun is the center of universe Planets and stars orbit around it Inferior planets have smaller orbits Retrograde motion happens when more inferior object lap other more superior object Still believe the concept of perfect heavenquot and refer to Ptolemaic model get decent predictions As complex as Ptolemaic model and not more accurate gt adding too much function Tycho Brahe 1546 1601 AD Known for his accurate and comprehensive astronomical and planetary observations Made the most accurate 1 arc minute naked eye measurements ever about planetary positions Observed a supernova in 1572 and a comet gt proved that it lay in the realm of heaven Still couldn t detect stellar parallax gt no telescope Earth is the center but other planets go around the Sun gt not many people take it seriously Johannes Kepler 1571 1630 AD Mathematician astronomer astrologer key figure in 17th century scientific revolution Greatest theorist at the time and is religious person Hired by Tycho as an apprentice gt begged him to find a system that support his observation Discover planetary motion model gt Kepler s law of planetary motion 0 First tried to match Tycho observation with circular orbits but an 8 arc minutes discrepancy led him to ellipses Ellipse Elongated circle 0 Amount ellipse stretches out is described by its eccentricity controlled by foci distance gt 2 focus point Kepler s first law 0 Orbit of each planet around Sun is an ellipse with Sun at one focus and nothing at the other 0 Distance of planet from Sun varies during its orbit Kepler s second law 0 As planet moves around its orbit it sweeps out equal areas in equal times 0 Near perihelion planet sweeps out an short wide area 0 Near aphelion planets sweeps out a long narrow area 0 Planet travels faster when it is nearer to the Sun and slower when it is farther Kepler s third law 0 More distant planets orbit the Sun at slower average speeds orbital period 2 average distance from Sun 3 Planetary motion might be the result of a force from Sun gt later proved as gravity by Newton Objections to Copernican view 0 Earth could not be moving because objects in air would be left behind Noncircular obits defied the perfect heavenquot concept 0 If Earth orbits the Sun stellar parallax will be detected Answered by Galileo gt solidify Copernican Revolution Refuting objections 0 Experiments that objects in air would stay with a moving Earth 0 Aristotle gt objects will naturally come to rest 0 Moving object remains in motion unless a force acts to stop it gt Newton s 1St law 0 Built a telescope in 1609 gt disprove perfect heavenquot concept 0 Saw sunspots on Sun mountains and craters on the Moon 0 Saw Milky Way turns into many stars gt stars are much farther than what Tycho argued and they don t have the same distance 0 Saw 4 moons orbiting Jupiter gt object that isn t orbiting the Earth existed Jupiter has its own system Galileo 0 Saw all phases of Venus gt Venus also orbits Sun Published Dialogue Concerning the Two Chief World Systemsquot 1632 At that time Catholic Church doctrine still held geocentric view Get into trial and ordered to annul his claim that Earth orbits Sun in 1633 by Catholic Church The book removed from Church s index of banned books in 1824 0 It s not being destroyed because the Church s scientists believe the value of his book but they can t do anything Formally vindicated by Church in 1992 Nature of Science 3 hallmarks of science 0 Modern science seeks explanations for observed phenomena that rely only on natural causes 0 Science advances with the creation and testing of models of nature that explain the observations as simply as possible 0 Complicated models will have more flaws gt replaced by the simpler one at some point 0 Applies to all kinds of disciplines 0 Scientific model must make testable predictions about natural phenomena gt revise or abandon the model if it s tested wrong Scientific theory is simple and powerful model that explains huge rang of observations with a few general principles and has attained the status of a theory by surviving repeated and varied testing gt fulfill all 3 hallmarks Motion Energy Gravity Speed rate at which an object moves ms Velocity speed direction ms Acceleration change in an object velocity either speed andor direction msAZ Acceleration of gravity 0 Falling objects accelerate at the same rate ignoring air resistance 0 Acceleration of Earth s gravity g 10 msAZ 0 Falling from higher height results in higher velocity when you hit the ground Momentum mass x velocity Force 0 Any influence that causes a free body to undergo acceleration 0 Rate of change of momentum 0 As long as the object s mass does not change the force causes acceleration o For multiple forces on object net force will change its momentum Mass amount of matter in object static Weight 0 Force that acts upon object dynamic 0 Object become weightless when freefalling Newton Physicist mathematician astronomer natural philosopher alchemist he succeeded to produce gold particle from solution but it s too small to be quantized theologian Realized the same physical laws that operate on Earth also operate in heavens one universe Discovered laws of motion and gravity 1687 Built 1St reflecting telescope Invented the mathematics of calculus Newton s first law of motion 0 Object moves at constant velocity unless a net force acts to change its speed or direction 0 First found by Galileo but no scientific interpretation Newton s second law of motion 0 Body of mass m subject to force F undergoes acceleration a in the same direction as the force and magnitude directly proportional to the force and inversely proportional to mass F m x a Newton s third law of motion 0 For every force there is always an equal and opposite reaction force 0 Objects always attract each other through gravity Conservation of angular momentum Object s angular momentum cannot change unless it transfers angular momentum to or from another object Angularcircling momentum mass x speed x radius Explains why planet keeps rotating and orbiting the Sun Kepler s 2nd law gt no transfer change in radius caused change in speed 0 Explains many spinning disks in universe galaxies materials around young stars etc 0 Kinetic energy of motion 0 Radiation energy carried by light 0 Potential stored energy 0 Gravitational Depends on object s mass and how far it can fall as a result of gravity In space object or gas cloud has more gravitational energy when it is spread out Contracting cloud converts gravitational energy to thermal energy 0 Massenergy Potential energy associated with object s mass E m x cAZ Small amount of mass can release a great deal of energy gt hydrogen bomb Concentrated energy can spontaneously turn into particles gt in particle accelerators 0 Thermal o Collective kinetic energy of many particles atoms and molecules moving randomly within a substance 0 Related to temperature but it is not the same temperature is the average rather than the collective Conservation of energy 0 Energy can be neither created nor destroyed Can change form or be exchanged between objects 0 Fundamental to science 0 Total energy content of universe was determined in Big Bang and remains the same today Universal law of gravity 0 Every mass attracts every other mass Attraction is directly proportional to the product of their masses and inversely proportional to the square of distance between their centers F G x massl x massZ distance 2 Newton showed that Kepler s laws are result of law of motion and universal law of gravity Newton discovered that Kepler s laws can be generalized First 2 laws apply to all orbiting objects Ellipses are not the only orbital paths gt boundellipses unbound parabolahyperbola Allows mass of distant object to be calculated if you can observe another object orbiting it 0 Measure orbital period and orbital distance by generalizing the third law gt orbital period 2 4 x piAZ x orbital distance 3 G x massl massZ Orbits Orbits Tides Tides Moo Orbital energy kinetic energy gravitational potential energy Orbits cannot change spontaneously gt conservation of energy Orbit can only change if it gains or loses energy from another object gt gravitational encounterslingshot assist maneuver altering the path and speed atmospheric drag Object that gains orbital energy moves into higher altitude orbit If object gains enough energy it may escape orbit changes from bound to unbound gt escape velocity Earth surface s escape velocity 11 kms Rise and fall twice each day every 12 hours 25 minutes Due to difference in the gravity between different parts of Earth and Moon Moon s pull on Earth is strongest on the side facing the Moon and weakest on the opposite gt stretchingtidal force Earth gets stretched along EarthMoon line Affects land and ocean Sun s effect on tides Tides vary with Moon s phase Spring tides gt Sun and Moon work together when new and full moon appeared Neap tides gt tidal forces from Sun and Moon counteract each other when first and thirdquarter moon appeared Moon rotates on its axis in exactly the same period that it takes to orbit Earth gt synchronous rotation Tidal force from Earth gives Moon 2 bulges along EarthMoon line Moon might rotated faster in the past Moon did rotate through its tidal bulges but gradually slowed gt tidal friction Finally it reaches synchronous rotation gt tidally locked Hardware Protection OS should protect hardware from illegal IO instructions andor OS memory access caused from program malfunction virus Dualmode operations Distinguish the instruction given to the hardware 2 mode of operations 0 User mode gt simple normal instruction from user 0 Monitorsupervisorsystemkernel mode gt hardware or important data access in OS memory 0 Make sure there is no illegal operation in kernel mode 0 Execute user process or OS process depends on the mode gt for example interrupt handling OS process 0 Mode bit is used to indicate the modes gt 0 monitor 1 user 0 System switch to monitor mode when there is interrupt or fault then back to user mode 0 Privileged instruction gt special instruction only for monitor mode IO protection 0 All IO instructions are privileged gt must go through OS 0 Protect from illegal IO operation gt read nonexistent file unauthorized access 0 OS handles a trap for illegal operation gt Java exceptions Memory proctection 0 Protect process instruction from being changed 0 ISR interrupt vector etc 0 Changed by virus or other processes 0 Define memory area for each program 0 Use 2 more registers Base gt save smallest legal physical memory address Limit gt save size of range Memory can only accessed in the stated region Load instructions for both registers are privileged If something failed trap is issued to OS OOOOO OS Services OS has multiple layers UI system calls services Services program execution file system etc are accessed using APIs called system calls It provides function such as UI gt command line CLI graphic user interface GUI batch Program execution gt load program to memory run terminate normalerror IO operation gt IO devicefile access requested Filesystem manipulation gt read and write create and delete search list information manage permission for files and directories System calls Provide interface between user program and OS Usually activated using assembly language but now available in highlevel using C C etc Execution require switch from user to kernel mode then back again after it ends Typically a number attached to every system call and is saved and indexed at a table along with its status and return values Caller has no information about the implementation 0 Obey API and understand OS action on resulting call 0 Managed by runtime support library gt done automatically hidden in background Process Process concept Program in execution gt dynamic Execution must be in a sequential order even though out of order execution is supported In memory 0 00000 Process state New Text gt code and program Data gt global variables global parameters Stack gt parameters and local variables in function Heap gt dynamically allocated variables Text and data is static fixed and usually at the bottom Stack grows from top and heap grows from bottom dynamic gt process is created allocate memory region and required resources Running gt execution of instruction Waiting gt waiting for specified event IO input etc Ready gt waiting to be assigned to CPU depends on scheduler Terminated gt end of execution There is a time in CPU If timer interrupt occur every 100ms the current process will be moved to ready state context switch The interrupt is generated every specified amount of time to increase CPU efficiency in multiprogramming timesharing system Process control block PCB Keep information related to every process Consists of O 0000 Pointer to other PCB gt PCB stored in the form of queue data structures Process state and numberid Program counter CPU registers Information for CPU scheduling memory management memory limit etc open files list of currently opened files etc Stored in main memory kernel space and get hardware protection gt change must happen in kernel mode Process memory is stored in user space Context switch 0 When CPU switches from a process to another OS save the statePCBinformation of old process and load the saved one for new process gt done in kernel mode 0 Time spends is considered overhead because it does not make progress in processing Schedang Types of queues 0 Job queue gt maintain processes with the same state in OS 0 Ready queue gt processes in ready state processes in memory waiting for CPU to execute them gt not waiting state only wait for CPU 0 Device queue gt processes waiting for access to that particular IO device Process moves between queues when it state changes All queues are saved in kernel space Each queue structure is located at its header gt pointer to head of first PCB and to tail of last PCB Scheduler Multiple schedulers is used to manage all the processes 0 Joblongterm scheduler 0 Select processes from disk and load them to memory 0 Decide the number of processes and which one to created and admitted to OS 0 Invoked infrequently every few secondsminutes 0 Do very advanced prediction on memory usage 0 Initially sets the number of processes in main memory that can be done with the current system degree of multi programming 0 CPUshortterm scheduler 0 Select process from memory and allocate CPU to it o Invoked frequently every 100ms gt fast decision maker Midterm scheduler gt adjust multiprogramming when system load is heavy o Swap out partially executed process to disk gt swap it back when the load is lighter 0 Use disk as virtual memory
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