The Mechanical Engineering And Metal Engineering Essay

The Mechanical Engineering And Metal Engineering Essay Metal fatigue is caused by repeated cycling of the load. It is a progressive localized damage due to fluctuating stresses and strains on the material. Metal fatigue cracks initiate and propagate in regions where the strain is most severe. This cyclic loading and crack initiation is represented using S-N curves. The Fig 1.1 consists of constant cyclic stress amplitude(S) which is applied to a specimen and the number of loading cycles (N) until the specimen fails is determined. The process fatigue failure is consists of three main stages. The first stage consists of initial crack initiation. The second stage consists of progressive crack growth across the part and the third and final stage consists of sudden fracture of the remaining cross section. The fatigue strength is the stress at which failure occurs for a given number of cycles, whereas the fatigue life is the number of cycles required material to fail. The most important concept of the S-N diagram is shown in Fig 1.1. This figure consists of S-N curves for Steel and Aluminium. (By Shawn M. Kelly) http://www.efunda.com/formulae/solid_mechanics/fatigue/images/fatigue_SN_01.gif Figure 1.1 S-N curves for steel and aluminium. The subject of fatigue testing is extensive, and is complicated by the important factors like the surface conditions of the specimen, the type of the stress variation, and the influence of the shape of the specimen on the stress flow. As it is known as that the highly polished specimens withstand better fatigue than the normal fatigue ones. The most damaging type of stress variation is the complete reversal, which is between the limit  ±Ãƒ Ã†â€™ for which the stress range is 2à Ã†â€™. Fluctuating stresses are less damaging, the standard case is between the limit 0 and +à Ã†â€™. For some materials such as aluminium, no endurance limit exists and therefore it should be planned lifetime of the structure to be less than the failure point. http://htmlimg1.scribdassets.com/izqlx4lamohzwzk/images/10-d0617ea942/000.jpg Figure 1.2 Fluctuating Stress Cycle. The above figure illustrates repeated stress cycle in which à Ã†â€™max (Rmax) is the maximum stress and à Ã†â€™min (Rmim) is the minimum stress and both are not equal. Here t is the time and à Ã†â€™a is the stress amplitude and à Ã†â€™m is the mean stress. In low fatigue cycle region (N In this experiment fatigue test for aluminium alloys of series 2000 have been conducted and described. S-N Curve Experiment for 6000 and 2000 Aluminium Alloys Series: The fatigue failure experiment is carried out for two different types of aluminium alloys i.e. 6082 and 2011 specimens. These experiments are carried in two different groups. A typical standard specimen is shown in Fig 1.3 as below. It is recommended to test at least 10 specimens of each type and they all must be cut from one length of the material. http://static.tecquipment.com/Products/RF1020_ALUMINIUM-FATIGUE-SPECIMEN.jpg Figure 1.3 Test Specimen. A set of bending stresses from 0.9 of the yield or proof stress to 0.4 of the ultimate strength is selected to match the number of the test specimens for the complete experiment. The setting up of the specimen on the machine is a reasonably simple operation which is done in proper methodology. The main object is to align the specimen and loading arm with the axis of rotation to eliminate stresses due to eccentric whirling of the specimen. Both in drive shaft and the loading arm chucks, loose collet grip is inserted. These inserts 9mm diameter ends of the test specimen are slid as shown in Fig. 1.4. http://www.twi.co.uk/twiimages/jk78f1.jpg Figure 1.4 Setting up of machine. ( by http://www.twi.co.uk/content/jk78.html) The collet is first tighten on the drive shaft chuck so that so that about 1 mm shoulder shows between the start of the neck and the face of the collet of the specimen. Then the loading arm is pushed on to the end of the specimen and adjusts the collet to give a sliding fit. The position of loading the loading arm is in such a way that the dimension of 109.5 mm is attained from the rear face of the bearing housing to the adjacent end of the neck of the specimen as shown in Fig 1.4 and finally tight the collet with the spanner. The specimen is rotated to check that the end of the cantilever run axially otherwise the specimen must get bend and can be discarded. Bearing Drive shaft and bearing Electric motor Chuck in which specimen is fitted. ON/OFF SwitchC:UsersasimDesktopall folderpicsmaterialsimagesattachments_16_12_2010DSC01501.JPG Figure 1.4 Rotating Fatigue Machine The counterbalance and load hangers should be ensured are in place. Switch motor ON and OFF to verify smooth running. The bending stress for the test is selected and required load or weight is applied on the load hanger. The revolution counter is set to zero before starting the machine and safety guard is used over the apparatus. The fracture time which might occur is estimated and noted. Endurance Limit: The stress value below which the material will withstand many number of load cycles. It is also known as fatigue limit. The stress level below which a specimen will withstand cyclic stress indefinitely without exhibiting fatigue failure. Rigid, elastic, low damping materials such as thermosetting plastics and some crystalline thermoplastics do not exhibit an endurance limit. Also known as  FATIGUE LIMIT.   (CRC Press LLC 1989) Ultimate stress: It is defined as the maximum/ultimate load under which a specimen breaks or fails. Stress corresponding to ultimate load is ultimate stress. Mean Stress: It is defined as the algebraic sum of maximum and minimum stress divided by 2. Ultimate Tensile Strength: In the given experiment ultimate tensile strength is calculated using the following formula p. Where p is the load applied to the material and is the stress. Recorded Data and Graph for 6000 series: Sample No. Load (N) Bending Stress (MPa) Result No. of Cycle Results (Fail/No- Fail) 1 11.25 225 21400 fail 2 10.6 212 114800 fail 3 9.95 199 115300 fail 4 9.3 186 293800 fail 5 8.65 173 161000 fail 6 8 160 184700 fail 7 7.35 147 905100 fail 8 6.7 134 2411100 fail 9 6.05 121 2765800 fail 10 5.9 118 3156700 fail Recorded Data and Graph for 2000 series: Sample No. Load (N) Bending Stress (MPa) Result No. of cycles (x100) Result (Fail/Not-fail) 1 13.5 270 95 Fail 2 12 240 407 Fail 3 10.5 210 482 Fail 4 9 180 1948 Fail 5 8.25 165 1781 Fail 6 7.5 150 2662 Fail 7 7.0 140 2165 Fail 8 6.0 120 4916 Fail 9 5.6 112 19970 Fail 10 5.2 104 More than 107 Not-fail 11 5 100 10 533 Fail 12 4.8 96 More than 107 Not-fail 13 4.6 92 14 4.6 92 More than 107 Not-fail 15 4 80 More than 107 Not-fail 2. Non-Destructive Testing Methods: 2.1 Introduction: Non-destructive testing (NDT) is a wide range of analysis technique used in science and industries to evaluate the properties of material or component and to detect the flaws in the material without causing damage. The non-destructive testing is the testing of the materials used to find surface or internal flaws or metallurgical conditions without interfering in the integrity of the materials. The flaw includes cracks or inclusions in welds and castings, or variations in structural properties which may lead to loss of strength and finally failure of materials. Non-destructive testing is used for measurement of components and spacing and for the measurement of physical properties such as internal stress and hardness. It is also used for in-service inspection and for conditions monitoring of operating plants. It is also used to look for sign of wear or internal changes on airplanes in aircraft industries. The NDT method is also a function part of quality control which is based on sampl ing analysis, this method is not just for rejecting the substandard material but gives assurance that it is good. The common types of Non-Destructive Testing are stated as follows: Magnetic Particle Inspection. Figure 2.1 Magnetic Particle Testing http://www.azom.com/work/8is7fjkADJ5v0JQByKTw_files/image003.gif Radiography Inspection. Figure 2.2 Radiography Testing. Ultrasonic Testing. Figure 2.3 Ultrasonic Testing. Liquid Penetrant Testing. Figure 2.4 Liquid Penetrant Testing. http://www.twi.co.uk/twiimages/ksijm001f1.gif Eddy Current Testing and Electro Magnetic Testing. Figure 2.5 Electro Magnetic Testing.http://www.eurondt.com/index_2.gif There are different types of non-destructive testing used for removing flaws as shown above but two main types of NDT on which experiments are perform are Magnetic particle testing and Ultrasonic Testing. 2.2 Magnetic Particle Testing: Introduction: Magnetic particle testing is type of non-destructive testing which is used for the detection of surface and near-surface flaws in the ferromagnetic materials and it is basically used for crack detection. Such flaws present in the magnetized part will cause a magnetic field, i.e. flux, to leave the part. It is however same as if there is a surface-breaking flaw in the specimen, the magnetic field is distorted, causing local magnetic flux leakage around the flaw. If the magnetic particles are applied to the surface of this specimen, the surface is covered by very fine iron particles and they will be held in the place by the flux leakage to give a visual indication. Figure 2.6 Deflection in the magnetic flux.http://www.ndt-ed.org/GeneralResources/MethodSummary/MT1.jpg http://www.milinc.com/images/magpartimgs/magpartdiag1.gif Thus a crack is indicated as a line or iron powder particles on the surface. The method of MPT is applicable to all metals which can be strongly magnetised such as ferritic steels, irons and some other alloys but not generally to austenitic steels. The modern equipments generate the magnetic field electrically either directly or indirectly. In direct method high ampere of current is passed through the specimen and magnetic flux is generated at right angle to the current flow. Therefore current flow is in the same direction of suspect defect. If this method is not possible to carry out because of the orientation of the defect, then the indirect method is used. This consists of two forms: Passing high current through a coil that encircles the specimen. Making the test piece form part of a yoke, this is surrounded by a current carrying coil. The effect is to pass magnetic flux along the part to reveal transverse and circumferential defects. Flux: It is a term which is used to refer the amount of magnetic field that exist at specific point within that field. It is measured in Webers. Flux Density: It is an indication of the strength of the magnetic field. It is represented by the lines of forces which are surrounded around the magnetic circuit, where the lines are closer to the flux. It is measured in Webbers/M2 or Telsa. Magnetic lines of force: These lines of force are imaginary lines which describes the path a free north pole would take in a magnetic field. These lines can be plotted using a compass. Experimental Procedure: Pump switch.The equipment used for performing the experiment is known as Johnson Allen NDT (SBU 2000). It should be sited on a firm concrete allowing access for servicing. The specimen provided contains five holes in it. The equipment should be connected to a 230 volt AC, 50Hz, 16 Amp power supply and Quick blow fuses should not be used. Connect Footswitch, Pump, and UV Light via socket to the equipment. Turn main supply on at the wall isolator. Turn the UV light ON and allow 10 mins to warm up. Slide out the ink hopper to within 75mm of the top flange with the Fluorescent Magnetic Ink and slide in the hopper gently. Turn the agitation ON and dispensing pump using the twist switch on the right of equipment. Figure 2.7 Magnetic Particles Testing Machine. Headstocks. Ink spray. Clamping knobs. C.F. control knob. Ammeter ON/OFF Switch.C:UsersasimDesktopall folderpicsmaterialsimagesIMG_0049.JPG Headstocks can be adjusted using the Clamping Knobs at the base. Once specimen is inserted and left side headstock is fixed then the specimen is ready to be tested. AC is current is used for surface defect and HWDC is used for all defect, so select the HWDC. Check the current control dial is turned to minimum. Experimental Precautions: The hole inside the given specimen should be clear otherwise the crack line does not come properly. Headstocks should be regularly checked. The specimen should be cleaned properly to prevent arcing and pitting on the surface. Circuits should be check regularly before performing any operation. Experimental Results: SpecimenThe given specimen contains 5 holes in it. The specimen is adjusted and fixed between the headstocks as shown in the figure below. Before performing the experiment the specimen should be clean properly other the line is not visible. As the hole was not clear and contains ink in it so the defect line is not obtained on the specimen. This can be seen in the figure below. Figure 2.8 Specimen without defect line Headstocks Ink spray.C:UsersasimDesktopall folderpicsmaterialsimagesattachments_16_12_2010DSC01541.JPG Then the holes are clean, and the experiment is performed again. When it is clean, the two defect lines are visible on the specimen. Hence, as the lines are seen on the specimen it can considered that it contains flaws in it. This works under the principle of right hand rule and so specimen has to be adjusted perpendicular to the headstocks so flux travel properly from the specimen and flaw. Testing Specimen. Defect lines. Figure 2.8 Specimen with visible defect line.C:UsersasimDesktopall folderpicsmaterialsimagesIMG_0060.JPG Advantages of Magnetic Particles Testing: It gives instant result and rapid inspection can be done for large surfaces. It is simple and easy to conduct. It detects a variety of surface and sub surface flaws, such as crack, porosity, inclusions, shrinkage, laps etc. Surface preparation is less critical than it is penetrant inspection. Sensitivity of testing can be specified and checked. It is economically cheap. Disadvantages of Magnetic Particles Testing: High currents applied to the components may cause damage. Smooth surface is required for application of this method. Materials which are tested must be ferromagnetic. Deep cracks or flaws are not detected. Materials may need to be demagnetized. Equipment is bulky and heavy. Material or part permeability may affect results. High power supply is needed for low surface. 2.3 Ultrasonic Testing: Introduction: Ultrasonic testing is a type of non-destructive testing method that uses high frequency sound waves (ultrasonic) which are above the range of human hearing and they are used to measure the geometric and physical properties of the materials. Ultrasonic waves travels at different velocities in different materials. There are different ways of sound travels through the material. One type of sound wave is called as compression or longitudinal travels which is at about 330m/s in air and 6400m/s in aluminium and approximately 5960m/s for steel. Figure 2.9 Ultrasonic Testing.http://www.energyworkforce.net/wp-content/uploads/ut1.jpg The pulsed beams of the ultrasound are used in a simplest instrument and a single probe (transducer) which is hand-held is paced on the surface of the specimen. An oscilloscope is connected to the probe which displays with the time-base the time that requires for an ultrasonic pulse to travel through the reflector which can be flaw, black surface etc. The height of the reflected pulse is related to the flaw size as seen from the transmitter probe which is displayed on oscilloscope screen. A single probe acts as both transmitter and receiver and hence the inspection can be done from one side of the specimen. Large grain material such as austenitic steel welding, copper casting etc., produce severe attenuation and are difficult to test but fine grain material such as forged material can be tested easily. Using the indication on the oscilloscope the size of the flaw can be determined. Ultrasonic attenuation and ultrasonic velocity measurements are used to study various material properti es. Experimental Procedure: A typical ultrasonic testing system consists of several functional units such as: Pulser/receiver. Transducer. Oscilloscope. Connecting wires. Couplant. Mild steel material (specimen). A pulser is an electronic device that can produce high voltage electrical pulses. From the high voltage pulses, transducer generates high frequency ultrasonic energy. This sound energy propagates through the material in the form of waves. Couplant. Transducer. Oscilloscope Figure 2.10 Setting up of Ultrasonic Testing.C:UsersasimDesktopall folderpicsmaterialsimagesattachments_16_12_2010DSC01547.JPGC:UsersasimDesktopall folderpicsmaterialsimagesattachments_16_12_2010DSC01545.JPG Mild steel specimen. Defects Display Screen The left side figure shows the cathode ray oscilloscope and the right side figure shows the mild steel material on the ultrasonic test is conducted. The given specimen was of mild steel with five holes in it. Before starting the experiment, the specimen should be properly clean. Then apply a couplant on it. Start the cathode ray oscilloscope. There are different button on oscilloscope such as gain, light, velocity, angle, dialog etc. as shown in figure below. Figure 2.11 various buttons on oscilloscope.C:UsersasimDesktopall folderpicsmaterialsimagesultrasonic8122010(002).jpg So it is adjusted in such a way that the deflection should be visible. The transducer is connected to the oscilloscope with the help of connecting wires. Then this transducer is placed on the specimen for testing the flaws in it. Experimental Observation: When the transducer is placed on the specimen it emits ultrasonic waves from the material (specimen). When the probe is placed on specimen it gives a very nice and high peak on the oscilloscope as shown in the below figure. It means that the ultrasonic waves travel easily from that part of the specimen and hence it does not have any flaw in that part. Figure 2.12 High peak signal in nice surface.C:UsersasimDesktopall folderpicsmaterialsimagesIMG_0065.JPG C:UsersasimDesktopall folderpicsmaterialsimagesultrasonicP081210_11.230001.jpg Similarly, when the probe is moved further on it can be seen in the oscilloscope that the highest peak is coming down and it nearly become nil or very low. It means that the high frequency waves are reflected. Hence it can be observed that, there is a flaw in that part of the specimen. It is the same part under which a big hole is there. Figure 2.13 Low peak signal in defective part.C:UsersasimDesktopall folderpicsmaterialsimagesIMG_0081.JPG C:UsersasimDesktopall folderpicsmaterialsimagesattachments_16_12_2010DSC01545.JPG Hence, from the above two figure it can be concluded that when there is high peak in oscilloscope there is no flaw at that part and similarly when the high peak decreases to low it means that part contains some flaw in it. Advantages of Ultrasonic Testing: The measurement is superior to other NDT methods. It is sensitive to both surface and subsurface discontinuities. It requires very minimal part preparations. It is highly accurate in determining reflector position and estimating size and shape. As the electronic equipment as used it give instantaneous results. It requires only single-sided access when the pulse-echo technique is used. It can also be used for other purposes such as thickness measurement etc. Disadvantages of Ultrasonic Testing: It normally requires a coupling medium to promote the transfer of sound energy into the test specimen. Those materials which are rough, very small, irregular in shape, thin or not homogeneous are very difficult to test. Surface must be accessible to transmit ultrasound. Cast iron and other grained materials are difficult to test due to their low sound transmission and high signal noise. Linear defects oriented parallel to the sound beam may go undetected. Feedback and Evaluation: S-N curve: The experiment S-N curve is used to determine the endurance fatigue limit of the material used in automotive industries. The given specimens were of aluminium alloys. There were two series of aluminium alloys i.e. 6000 series and 2000 series on which experiments are performed. Ten samples of each specimen were given. This experiment was performed in two groups. One group perform the experiment on 6082 specimen and other group perform the experiment on 2011 specimen. In this experiment weights are taken in Newton and the number of cycles is shown on the machine. Corresponding to this stress/load (S) and number of cycles (N), S-N curve is plotted. When the load is high it number of cycles is low and when the load is decreased its number of cycles increases. This is shown in graphs below. This is a S-N curve graph for 6011 aluminium alloy (specimen). From the above graph it can be seen that at high stress/load i.e. 225 MPa or 11.25N. The number of cycles is 21400. As the stress goes on increasing the number of cycles goes on decreasing. Hence the endurance fatigue limit varies at different load for the same specimen. When the specimen fails it is taken out from the chuck and it can be checked microscope and the cracks can be seen properly. From this the physical properties of the material can be checked and the fatigue limit can be obtained. There are some microscopic images of specimens, they are as follows: Sample 1 at 11.25N load. C:UsersasimDesktopall folderpicsmaterialsimagesultrasonicsamplemicroscopicimages- sncurveSample1_1.JPGC:UsersasimDesktopall folderpicsmaterialsimagesultrasonicsamplemicroscopicimages- sncurveSample1_2.JPG Sample 2 at 10.6N load. C:UsersasimDesktopall folderpicsmaterialsimagesultrasonicsamplemicroscopicimages- sncurveSample2_1.JPGC:UsersasimDesktopall folderpicsmaterialsimagesultrasonicsamplemicroscopicimages- sncurveSample2_2.JPG There are many more microscopic images which look similar to the above images and it fails at different loads. The below figure is of the specimen before experiment. http://static.tecquipment.com/Products/RF1020_ALUMINIUM-FATIGUE-SPECIMEN.jpg This specimen is fixed between the chucks and when the experiment is performed at different loads the specimen which is fixed between the chuck breaks. This is shown in the figure below. C:UsersasimDesktopall folderpicsmaterialsimagesIMG_0040.JPG It can be clearly seen from the previous figure that the specimen breaks from its middle. First the crack propagates in it and then its finally fails. The graph below is the S-N curve graph for 2011 aluminium alloy specimen which is experimented by other group. This graph start from 270Mpa and the applied on the specimen is 13.5 N and therefore the number of cycles perform by the specimen is less i.e. 9500. These two specimens cannot be compared as both the group has taken different values of stress and therefore the number of cycles are different both the specimens. From the given ten samples, the discussion of the fatigue limit is nearly impossible as we find the scatter point graph not a perfect curve of S-N. For establishing the endurance fatigue limit of both the specimens more experiments must be conducted on it. Also the specimen should be properly fixed in the chuck otherwise it fails in somewhere before the expected value. Magnetic Particles Testing: This experiment is performed to check the flaws i.e. cracks, holes, black surface of the materials. This experiment comes under non-destructive testing. A specimen of mild steel is given and it contains five holes in it. This specimen is fixed in Johnson Allen NDT machine. This specimen is fixed between the headstocks of the machine. The specimen is fixed perpendicular to the headstocks. The perpendicular arrangement of headstock and specimen is done because this machine works under the principle of right hand rule and it generates flux into the specimen. This flux passes through the material. When there is any flaw into the material the flux gets affected and a black line of iron particles is seen on the surface of the material. In this experiment also the specimen contains five holes in it and a black line of iron particles is seen on the surface of the material. The current is control with the help of C.F. control switch. The black defect line on the specimen can be seen in figure below. The amount of flux running through the specimen can be measured with the help of ammeter. But the ammeter in the machine under which this testing is performed was not working. So the exact amount of flux generated in specimen cannot be measured. The ammeter and C.F. control switch is shown in the figure below. C.F. control switch. AmmeterC:UsersasimDesktopall folderpicsmaterialsimagesIMG_0045.JPG Ultrasonic testing: This type of testing is also used to detect flaws and crack inside the material without damaging it. The specimen provided is a mild steel slab and it contains holes in it. It can be seen that when there is no flaw inside the specimen it shows high peak on the oscilloscope and similarly when there is any flaw the ultrasonic waves get reflected and the high peak decreases to low peak. This is clearly in figures below. C:UsersasimDesktopall folderpicsmaterialsimagesIMG_0065.JPGC:UsersasimDesktopall folderpicsmaterialsimagesIMG_0081.JPG Conclusion: From the above experiments we can conclude that S-N curve is best method to determine the fatigue limit but it cant be done using ten samples as it does not gives the proper curve graph for the specimen. Magnetic Particle Testing is a good way of finding flaws from the materials without damaging it but the machine is not that comfortable and more precautions must be used before using it otherwise the flaws are not detected. Similarly Ultrasonic Testing is a good way cracks and other flaws detecting and these are used in aircraft industries. Referencing: Mark Wilcox and George Downes, A brief description of NDT techniques Available at: http://www.turkndt.org/sub/makale/ornek/a%20brief%20description%20of%20NDT.pdf [Accessed on:3 Dec 2010] www.ndted.org.com NDT Method Summary Available at: http://www.ndt-ed.org/GeneralResources/MethodSummary/MethodSummary.htm [Accessed on:12 Dec 2010] www.insight-ndt.com (2007). Qualiron ductile iron metal quality tester. Available: http://www.insight-ndt.com/ultrasonic/qualiron.html. [Last accessed 3rd dec 2010.] www.NDT.net Non-destructive Material Testing with Ultrasonics Introduction to the Basic Principles Available at: http://www.ndt.net/article/v05n09/berke/berke1.htm [Accessed on:15 Dec 2010] www.materialsengineer.com (2007) Metallurgical Fatigue Failures Available at http://www.materialsengineer.com/CA-fatigue.htm [Last accessed on 3rd Dec 2010] www.sv.vt.edu (1997). By Shawn M. Kelly, Fatigue, Available at http://www.sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/anal/kelly/fatigue.html [Accessed on 6 Dec 2010]. www.scribd.com Fatigue Failure Available at http://www.scribd.com/doc/29476995/fatigue-failure [Accessed on 8 Dec]. www.key-to-metals.com.cn (99-2000) Fatigue of metals (stress cycles) Available at http://www.key-to-metals.com.cn/page.aspx?ID=CheckArticlesite=ktsNM=281 [Accessed on 8 Dec]. www.twi.co.uk (2005) Fatigue Testing Available at http://www.twi.co.uk/content/jk78.html [Accessed on 12 Dec]. www.azom.com (2010) Non-destructive Testing-Surface Examination Techniques. http://www.azom.com/Details.asp?ArticleID=522 [Accessed on 13 Dec]. www.energyworkforce.net (2010) Principles of Ultrasonic Testing. Available at http://www.energyworkforce.net/?p=126 [Accessed on 16 Dec].

Digital Fortress Chapter 59-62

Chapter 59 Susan reached for Commander Strathmore's hand as he helped her up the ladder onto the Crypto floor. The image of Phil Chartrukian lying broken on the generators was burned into her mind. The thought of Hale hiding in the bowels of Crypto had left her dizzy. The truth was inescapable-Hale had pushed Chartrukian. Susan stumbled past the shadow of TRANSLTR back toward Crypto's main exit-the door she'd come through hours earlier. Her frantic punching on the unlit keypad did nothing to move the huge portal. She was trapped; Crypto was a prison. The dome sat like a satellite, 109 yards away from the main NSA structure, accessible only through the main portal. Since Crypto made its own power, the switchboard probably didn't even know they were in trouble. â€Å"The main power's out,† Strathmore said, arriving behind her. â€Å"We're on aux.† The backup power supply in Crypto was designed so that TRANSLTR and its cooling systems took precedence over all other systems, including lights and doorways. That way an untimely power outage would not interrupt TRANSLTR during an important run. It also meant TRANSLTR would never run without its freon cooling system; in an uncooled enclosure, the heat generated by three million processors would rise to treacherous levels-perhaps even igniting the silicon chips and resulting in a fiery meltdown. It was an image no one dared consider. Susan fought to get her bearings. Her thoughts were consumed by the single image of the Sys-Sec on the generators. She stabbed at the keypad again. Still no response. â€Å"Abort the run!† she demanded. Telling TRANSLTR to stop searching for the Digital Fortress pass-key would shut down its circuits and free up enough backup power to get the doors working again. â€Å"Easy, Susan,† Strathmore said, putting a steadying hand on her shoulder. The commander's reassuring touch lifted Susan from her daze. She suddenly remembered why she had been going to get him. She wheeled, â€Å"Commander! Greg Hale is North Dakota!† There was a seemingly endless beat of silence in the dark. Finally Strathmore replied. His voice sounded more confused than shocked. â€Å"What are you talking about?† â€Å"Hale†¦Ã¢â‚¬  Susan whispered. â€Å"He's North Dakota.† There was more silence as Strathmore pondered Susan's words. â€Å"The tracer?† He seemed confused. â€Å"It fingered Hale?† â€Å"The tracer isn't back yet. Hale aborted it!† Susan went on to explain how Hale had stopped her tracer and how she'd found E-mail from Tankado in Hale's account. Another long moment of silence followed. Strathmore shook his head in disbelief. â€Å"There's no way Greg Hale is Tankado's insurance! It's absurd! Tankado would never trust Hale.† â€Å"Commander,† she said, â€Å"Hale sank us once before-Skipjack. Tankado trusted him.† Strathmore could not seem to find words. â€Å"Abort TRANSLTR,† Susan begged him. â€Å"We've got North Dakota. Call building security. Let's get out of here.† Strathmore held up his hand requesting a moment to think. Susan looked nervously in the direction of the trapdoor. The opening was just out of sight behind TRANSLTR, but the reddish glow spilled out over the black tile like fire on ice. Come on, call Security, Commander! Abort TRANSLTR! Get us out of here! Suddenly Strathmore sprang to action. â€Å"Follow me,† he said. He strode toward the trapdoor. â€Å"Commander! Hale is dangerous! He-â€Å" But Strathmore disappeared into the dark. Susan hurried to follow his silhouette. The commander circled around TRANSLTR and arrived over the opening in the floor. He peered into the swirling, steaming pit. Silently he looked around the darkened Crypto floor. Then he bent down and heaved the heavy trapdoor. It swung in a low arc. When he let go, it slammed shut with a deadening thud. Crypto was once again a silent, blackened cave. It appeared North Dakota was trapped. Strathmore knelt down. He turned the heavy butterfly lock. It spun into place. The sublevels were sealed. Neither he nor Susan heard the faint steps in the direction of Node 3. Chapter 60 Two-tone headed through the mirrored corridor that led from the outside patio to the dance floor. As he turned to check his safety pin in the reflection, he sensed a figure looming up behind him. He spun, but it was too late. A pair of rocklike arms pinned his body face-first against the glass. The punk tried to twist around. â€Å"Eduardo? Hey, man, is that you?† Two-Tone felt a hand brush over his wallet before the figure leaned firmly into his back. â€Å"Eddie!† the punk cried. â€Å"Quit fooling around! Some guy was lookin' for Megan.† The figure held him firmly. â€Å"Hey, Eddie, man, cut it out!† But when Two-Tone looked up into the mirror, he saw the figure pinning him was not his friend at all. The face was pockmarked and scarred. Two lifeless eyes stared out like coal from behind wire-rim glasses. The man leaned forward, placing his mouth against Two-Tone's ear. A strange, voice choked, â€Å"Adonde fue? Where'd he go?† The words sounded somehow misshapen. The punk froze, paralyzed with fear. â€Å"Adonde fue?† the voice repeated. â€Å"El Americano.† â€Å"The†¦ the airport. Aeropuerto,† Two-Tone stammered. â€Å"Aeropuerto?† the man repeated, his dark eyes watching Two-Tone's lips in the mirror. The punk nodded. â€Å"Tenia el anillo? Did he have the ring?† Terrified, Two-Tone shook his head. â€Å"No.† â€Å"Viste el anillo? Did you see the ring?† Two-Tone paused. What was the right answer? â€Å"Viste el anillo?† the muffled voice demanded. Two-Tone nodded affirmatively, hoping honesty would pay. It did not. Seconds later he slid to the floor, his neck broken. Chapter 61 Jabba lay on his back lodged halfway inside a dismantled mainframe computer. There was a penlight in his mouth, a soldering iron in his hand, and a large schematic blueprint propped on his belly. He had just finished attaching a new set of attenuators to a faulty motherboard when his cellular phone sprang to life. â€Å"Shit,† he swore, groping for the receiver through a pile of cables. â€Å"Jabba here.† â€Å"Jabba, it's Midge.† He brightened. â€Å"Twice in one night? People are gonna start talking.† â€Å"Crypto's got problems.† Her voice was tense. Jabba frowned. â€Å"We been through this already. Remember?† â€Å"It's a power problem.† â€Å"I'm not an electrician. Call Engineering.† â€Å"The dome's dark.† â€Å"You're seeing things. Go home.† He turned back to his schematic. â€Å"Pitch black!† she yelled. Jabba sighed and set down his penlight. â€Å"Midge, first of all, we've got aux power in there. It would never be pitch black. Second, Strathmore's got a slightly better view of Crypto than I do right now. Why don't you call him?† â€Å"Because this has to do with him. He's hiding something.† Jabba rolled his eyes. â€Å"Midge sweetie, I'm up to my armpits in serial cable here. If you need a date, I'll cut loose. Otherwise, call Engineering.† â€Å"Jabba, this is serious. I can feel it.† She can feel it? It was official, Jabba thought, Midge was in one of her moods. â€Å"If Strathmore's not worried, I'm not worried.† â€Å"Crypto's pitch black, dammit!† â€Å"So maybe Strathmore's stargazing.† â€Å"Jabba! I'm not kidding around here!† â€Å"Okay, okay,† he grumbled, propping himself up on an elbow. â€Å"Maybe a generator shorted out. As soon as I'm done here, I'll stop by Crypto and-â€Å" â€Å"What about aux power!† Midge demanded. â€Å"If a generator blew, why is there no aux power?† â€Å"I don't know. Maybe Strathmore's got TRANSLTR running and aux power is tapped out.† â€Å"So why doesn't he abort? Maybe it's a virus. You said something earlier about a virus.† â€Å"Damn it, Midge!† Jabba exploded. â€Å"I told you, there's no virus in Crypto! Stop being so damned paranoid!† There was a long silence on the line. â€Å"Aw, shit, Midge,† Jabba apologized. â€Å"Let me explain.† His voice was tight. â€Å"First of all, we've got Gauntlet-no virus could possibly get through. Second, if there's a power failure, it's hardware-related-viruses don't kill power, they attack software and data. Whatever's going on in Crypto, it's not a virus.† Silence. â€Å"Midge? You there?† Midge's response was icy. â€Å"Jabba, I have a job to do. I don't expect to be yelled at for doing it. When I call to ask why a multi billion-dollar facility is in the dark, I expect a professional response.† â€Å"Yes, ma'am.† â€Å"A simple yes or no will suffice. Is it possible the problem in Crypto is virus-related?† â€Å"Midge†¦ I told you-â€Å" â€Å"Yes or no. Could TRANSLTR have a virus?† Jabba sighed. â€Å"No, Midge. It's totally impossible.† â€Å"Thank you.† He forced a chuckle and tried to lighten the mood. â€Å"Unless you think Strathmore wrote one himself and bypassed my filters.† There was a stunned silence. When Midge spoke, her voice had an eerie edge. â€Å"Strathmore can bypass Gauntlet?† Jabba sighed. â€Å"It was a joke, Midge.† But he knew it was too late. Chapter 62 The Commander and Susan stood beside the closed trapdoor and debated what to do next. â€Å"We've got Phil Chartrukian dead down there,† Strathmore argued. â€Å"If we call for help, Crypto will turn into a circus.† â€Å"So what do you propose we do?† Susan demanded, wanting only to leave. Strathmore thought a moment. â€Å"Don't ask me how it happened,† he said, glancing down at the locked trapdoor, â€Å"but it looks like we've inadvertently located and neutralized North Dakota.† He shook his head in disbelief. â€Å"Damn lucky break if you ask me.† He still seemed stunned by the idea that Hale was involved in Tankado's plan. â€Å"My guess is that Hale's got the pass-key hidden in his terminal somewhere-maybe he's got a copy at home. Either way, he's trapped.† â€Å"So why not call building security and let them cart him away?† â€Å"Not yet,† Strathmore said, â€Å"if the Sys-Secs uncover stats of this endless TRANSLTR run, we've got a whole new set of problems. I want all traces of Digital Fortress deleted before we open the doors.† Susan nodded reluctantly. It was a good plan. When Security finally pulled Hale from the sublevels and charged him with Chartrukian's death, he probably would threaten to tell the world about Digital Fortress. But the proof would be erased-Strathmore could play dumb. An endless run? An unbreakable algorithm? But that's absurd! Hasn't Hale heard of the Bergofsky Principle? â€Å"Here's what we need to do.† Strathmore coolly outlined his plan. â€Å"We erase all of Hale's correspondence with Tankado. We erase all records of my bypassing Gauntlet, all of Chartrukian's Sys-Sec analysis, the Run-Monitor records, everything. Digital Fortress disappears. It was never here. We bury Hale's key and pray to God David finds Tankado's copy.† David, Susan thought. She forced him from her mind. She needed to stay focused on the matter at hand. â€Å"I'll handle the Sys-Sec lab,† Strathmore said. â€Å"Run-Monitor stats, mutation activity stats, the works. You handle Node 3. Delete all of Hale's E-mail. Any records of correspondence with Tankado, anything that mentions Digital Fortress.† â€Å"Okay,† Susan replied, focusing. â€Å"I'll erase Hale's whole drive. Reformat everything.† â€Å"No!† Strathmore's response was stern. â€Å"Don't do that. Hale most likely has a copy of the pass-key in there. I want it.† Susan gaped in shock. â€Å"You want the pass-key? I thought the whole point was to destroy the pass-keys!† â€Å"It is. But I want a copy. I want to crack open this damn file and have a look at Tankado's program.† Susan shared Strathmore's curiosity, but instinct told her unlocking the Digital Fortress algorithm was not wise, regardless of how interesting it would be. Right now, the deadly program was locked safely in its encrypted vault-totally harmless. As soon as he decrypted it†¦. â€Å"Commander, wouldn't we be better off just to-â€Å" â€Å"I want the key,† he replied. Susan had to admit, ever since hearing about Digital Fortress, she'd felt a certain academic curiosity to know how Tankado had managed to write it. Its mere existence contradicted the most fundamental rules of cryptography. Susan eyed the commander. â€Å"You'll delete the algorithm immediately after we see it?† â€Å"Without a trace.† Susan frowned. She knew that finding Hale's key would not happen instantly. Locating a random pass-key on one of the Node 3 hard drives was somewhat like trying to find a single sock in a bedroom the size of Texas. Computer searches only worked when you knew what you were looking for; this pass-key was random. Fortunately, however, because Crypto dealt with so much random material, Susan and some others had developed a complex process known as a nonconformity search. The search essentially asked the computer to study every string of characters on its hard drive, compare each string against an enormous dictionary, and flag any strings that seemed nonsensical or random. It was tricky work to refine the parameters continually, but it was possible. Susan knew she was the logical choice to find the pass-key. She sighed, hoping she wouldn't regret it. â€Å"If all goes well, it will take me about half an hour.† â€Å"Then let's get to work,† Strathmore said, putting a hand on her shoulder and leading her through the darkness toward Node 3. Above them, a star-filled sky had stretched itself across the dome. Susan wondered if David could see the same stars from Seville. As they approached the heavy glass doors of Node 3, Strathmore swore under his breath. The Node 3 keypad was unlit, and the doors were dead. â€Å"Damn it,† he said. â€Å"No power. I forgot.† Strathmore studied the sliding doors. He placed his palms flat against the glass. Then he leaned sideways trying to slide them open. His hands were sweaty and slipped. He wiped them on his pants and tried again. This time the doors slid open a tiny crack. Susan, sensing progress, got in behind Strathmore and they both pushed together. The doors slid open about an inch. They held it a moment, but the pressure was too great. The doors sprang shut again. â€Å"Hold on,† Susan said, repositioning herself in front of Strathmore. â€Å"Okay, now try.† They heaved. Again the door opened only about an inch. A faint ray of blue light appeared from inside Node 3; the terminals were still on; they were considered critical to TRANSLTR and were receiving aux power. Susan dug the toe of her Ferragamo's into the floor and pushed harder. The door started to move. Strathmore moved to get a better angle. Centering his palms on the left slider, he pushed straight back. Susan pushed the right slider in the opposite direction. Slowly, arduously, the doors began to separate. They were now almost a foot apart. â€Å"Don't let go,† Strathmore said, panting as they pushed harder. â€Å"Just a little farther.† Susan repositioned herself with her shoulder in the crack. She pushed again, this time with a better angle. The doors fought back against her. Before Strathmore could stop her, Susan squeezed her slender body into the opening. Strathmore protested, but she was intent. She wanted out of Crypto, and she knew Strathmore well enough to know she wasn't going anywhere until Hale's pass-key was found. She centered herself in the opening and pushed with all her strength. The doors seemed to push back. Suddenly Susan lost her grip. The doors sprang toward her. Strathmore fought to hold them off, but it was too much. Just as the doors slammed shut, Susan squeezed through and collapsed on the other side. The commander fought to reopen the door a tiny sliver. He put his face to the narrow crack. â€Å"Jesus, Susan-are you okay?† Susan stood up and brushed herself off. â€Å"Fine.† She looked around. Node 3 was deserted, lit only by the computer monitors. The bluish shadows gave the place a ghostly ambiance. She turned to Strathmore in the crack of the door. His face looked pallid and sickly in the blue light. â€Å"Susan,† he said. â€Å"Give me twenty minutes to delete the files in Sys-Sec. When all traces are gone, I'll go up to my terminal and abort TRANSLTR.† â€Å"You better,† Susan said, eyeing the heavy glass doors. She knew that until TRANSLTR stopped hoarding aux power, she was a prisoner in Node 3. Strathmore let go of the doors, and they snapped shut. Susan watched through the glass as the commander disappeared into the Crypto darkness.

Should Everyone Undertake University

ASSIGNMENT: REFERENCED ESSAY TITTLE: EDUCATION TOPIC 1: SHOULD EVERYONE BE REQUIRED TO UNDERTAKE A UNIVERSITY EDUCAtion DATE: 6 JANUARY 2013 In modern life, many students choose to enter university or college after they have graduated high school because higher education is a good environment to prepare for their future. However, some others think that it is only one of causes to increase the rate of unemployment, while they just need to follow vocational training or start working to improve their skills.This essay argues that everyone should be required to undertake a university education because it gives benefit to individuals such as career opportunities with higher earnings and social benefits. One of the main reasons why people should go to university is because it is a personal investment that can improve their life’s quality in the future. In higher education, people not only learn the knowledge from books but they also acquire what they need to know for their future li fe.Potter (2006) states that â€Å"university graduates also enjoy lots of other non-market benefits, including a lifetime of better mental and physical health, stronger social networks, and higher social status†. Indeed, university education provides many opportunities and benefits. Firstly, higher education provides career opportunities for students because they can get more knowledge and experience for their jobs in the future. Lederer (2010) mentions that university students will have lower unemployment rates in an economic downturn.This means as job markets are growing up, there are hundreds of applicants for one position in a company so if people do not have a qualification from university or college, it will be hard for them to be accepted. Furthermore, individual income is also strongly related to education attainment. People who graduate higher education may earn more than others so they will have more employer provided health and pension benefits. For example, accor ding to Baum (2007) â€Å"the typical bachelor’s degree recipient can expect to earn about 61% more over 40 years working life than the typical high school graduate earning over the same period†.Some students believe that vocational training might be seen alternative program for university. However, they can still find a good job, their company will require college or university experience if they want to have a higher salary. Finally, higher education is where students build connected networks. They may meet friends and mentors that become a future contact and colleagues from all activities when learning including volunteer work, summer jobs or student organizations. The author in the article â€Å"building rapport-establishing bonds† states that developing professional connection is a skill that everyone can learn and can use easily.They can use it to bring countless opportunities to be successful. Consequently, studying higher education will make more new opp ortunities for student to have a better life and prepare for their career. Next, undertaking university education is not just benefitcal for individual students but also beneficial to the whole society. People, who have higher learning, will have awareness and responsibility for their life. Firstly, going to university is related to economic advantages of society.Baum (2007) presents: â€Å"higher levels of education lead to both higher of earning for individuals and higher taxes revenues for federal, state, and local governments†. University graduates not only pay more taxes with higher income, but they also tend to have better health and depend less on government programs and spend more leisure time with their family or on civic activities. Moreover, students who have higher education will have more knowledge and awareness in life choices and can more easily to avoid lack of money and will become a criminal. According to Dr.Hill (2005), educational attainment may lead to le ss criminal behavior and lower imprisonment rate. Thus, the number of criminals will decline so human life will be happier and people no longer worried about things such as phishing, theft or violence. Higher education is a good way to help develop the economy and society. In conclusion, everyone should be required to undertake university education because students can have the opportunity to prepare for their jobs, creating career opportunities and higher income in the future. This leads to better individual life’s quality and give more benefits for society.Overall, from reasons above, students should be encouraged to go to university to get better life and better country. REFERENCE LIST: Baum and Payea, 2005, ‘the benefits of higher education for individuals and society’, College Board, vol. 1, page 10 and 16, viewed 6 January 2013 http://www. collegeboard. com/prod_downloads/about/news_info/trends/ed_pays_2007. pdf ‘Building rapport-establishing bondsâ⠂¬â„¢, mind tools, viewed 6 January 2013 http://www. mindtools. com/pages/article/building-rapport. htm Hill Ph. D, Hoffman Ph. D and Rex MBA, 2005, ‘the value of higher education: individual and societal benefit’, school of business, vol. , page 24, viewed 6 January 2013 http://wpcarey. asu. edu/seid/upload/Value%20Full%20Report_final_october%202005a. pdf Lederer, J 2010, â€Å"Job Growth: Why increasing education attainment is so important for creating jobs†, Washington Higher Education Coordinating Board, viewed 6 January 2013 http://www. wsac. wa. gov/sites/default/files/TAB7A-JobGrowthPresentation. pdf Potter, A 2006, â€Å"should everyone go to university? †, reading pack, vol. 6, viewed 6 January 2013 http://www. macleans. ca/education/universities/article. jsp? content=20061113_136513_136513

Learn the French Conjugations for Présenter (to Present)

The French verb  prà ©senter  means to introduce or to present. While its easy enough to remember because its similar to the English, you will still need to conjugate it to say presented or introducing. The good news is that this is a regular verb and a brief lesson will introduce you to its most important conjugations.   The Basic Conjugations of  Prà ©senter French verb conjugations tend to worry French students because you have so many words to memorize. Where English gives us only a few verb forms for the present, future, and past tenses, French gives us a new word for each subject pronoun within each tense. However, with a word like  prà ©senter, which  is a  regular -er verb, the conjugations are just a little easier. Thats because it follows the most common conjugation pattern found in the French language. If youve studied a few verbs already, the endings you see here should look familiar. The indicative verb mood is the most common and it includes the basic tenses youll need for most conversations. Using the chart, you can find the appropriate conjugation that corresponds to the subject and the tense of your sentence. As an example,  je prà ©sente  means I am presenting while  nous prà ©sentions  means we introduced. Present Future Imperfect je prsente prsenterai prsentais tu prsentes prsenteras prsentais il prsente prsentera prsentait nous prsentons prsenterons prsentions vous prsentez prsenterez prsentiez ils prsentent prsenteront prsentaient The Present Participle of  Prà ©senter For regular verbs, forming the  present participle  is simple. Just add  -ant  to the verb stem and you have the word  prà ©sentant. Prà ©senter  in the Compound Past Tense While you can use the imperfect for the past tense, you may find the  passà © composà ©Ã‚  easier to remember. This is a compound that requires the  past participle  prà ©sentà ©, which tells us that the act of introducing has already happened. The only conjugation you need to worry about here is transforming  the auxiliary verb  avoir  into the present tense. Youll then follow that with  prà ©sentà ©. For example, I introduced is  jai prà ©sentà ©Ã‚  and we introduced is  nous avons prà ©sentà ©. More Simple Conjugations of  Prà ©senter While the forms of  prà ©senter  above should be your focus at first, there are a few more simple conjugations you may need at times. For example,  the subjunctive  is helpful when you need to question the act of introducing and  the conditional  is used when its dependent on something else. Both  the passà © simple  and  the imperfect subjunctive  are literary forms and typically only found in written French. Subjunctive Conditional Pass Simple Imperfect Subjunctive je prsente prsenterais prsentai prsentasse tu prsentes prsenterais prsentas prsentasses il prsente prsenterait prsenta prsentt nous prsentions prsenterions prsentmes prsentassions vous prsentiez prsenteriez prsenttes prsentassiez ils prsentent prsenteraient prsentrent prsentassent You may not need  the imperative  for a verb like  prà ©senter  often, but its good to know that when you do use it the subject pronoun is not required. Imperative (tu) prsente (nous) prsentons (vous) prsentez