International Journal of Engineering Education | Year: 2012
DC-DC converters have a wide usage as the driver circuit of direct current (DC) motors. This has necessitated sensitive speed controls to be made on DC motors. Classical controllers have lower performance due to the non-linear features of DCmotors, such as saturation and friction. The Neural Network Controllers (NNC) are widely used in controlling poorlydefined nonlinear and uncertain systems. NNCcourses are now being offered by several universities at the bachelor0s and master's degree levels as a result of NNC's successful applications in these fields. However, the training of an NNC driver circuit in a laboratory environment is a time-consuming and expensive task. In this study, an NNC training set of the DC converter-fed Permanent Magnet Direct Current (PMDC) motor, which is part of the electrical machinery courses, was prepared. The set has a flexible structure and a graphical interface. Thanks to this set, it has become possible to change the PMDC motor and controller parameters, and monitor the system's reaction under various operational conditions in graphics. This training set can also guarantee effective learning and comprehension of Artificial Neural Networks (ANN). © 2012 TEMPUS Publications.
International Journal of Physical Sciences | Year: 2010
Direct current (DC) motors have currently a wide usage in industrial applications. This resulted in the necessity of making the speed controls of DC motors in a sensitive manner. Conventional controllers have poorer performances due to the non-linear features of DC motors like saturation and friction. Fuzzy logic controllers (FLC) are widely used in controlling poorly-defined, nonlinear and imprecise systems. FLC courses are being given in many universities at the graduate and/or postgraduate levels due to FLC achievements in these areas. The education of a FLC driver in a lab environment is a timeconsuming and expensive task. In this study, a virtual lab is prepared for the FLC of a permanent magnet direct current (PMDC) motor, which is a part of the electrical machines course. It is a software having a flexible structure and a graphical user interface (GUI). The virtual lab allows as a software tool monitoring the system's reaction in different operation conditions through graphs by changing the PMDC motor and controller parameters. ©2010 Academic Journals.
News Article | December 5, 2016
Large areas of the global ocean, so called marine "dead zones" contain no oxygen and support microbial processes that remove vast amounts of nitrogen from the global ocean. Nitrogen is a key nutrient for life. These dead zones are well known off the western coasts of North and South America, off the coast of Namibia and off the west coast of India in the Arabian Sea. New research published in the journal Nature Geoscience shows that the Bay of Bengal, located in the northeastern Indian Ocean, also hosts a "dead zone" of an estimated 60,000 km2 and occupying water depths of between 100 and 400 meters. This research was conducted as cooperation between the University of Southern Denmark (SDU), the Max Planck Institute (MPI) for Marine Microbiology in Bremen and the National Institute of Oceanography (NIO) of India. Lead author of the study Laura Bristow, a former postdoc at SDU and now a scientist at the MPI explains "the Bay of Bengal has long stood as an enigma because standard techniques suggest no oxygen in the waters, but, despite this, there has been no indication of nitrogen loss as in other 'dead zones' of the global ocean". Using newly developed oxygen-sensing technology, the researchers demonstrated that some oxygen does exist in the Bay of Bengal waters, but at concentrations much less than standard techniques could detect and some 10,000 times less than found in the air-saturated surface waters. The researchers also discovered that the Bay of Bengal hosts microbial communities that can remove nitrogen, as in other well-known "dead zones" and even some evidence that they do remove nitrogen, but at really slow rates. Bristow continues "we have this crazy situation in the Bay of Bengal where the microbes are poised and ready to remove lots more nitrogen than they do, but the trace amounts of oxygen keep them from doing so". Wajih Naqvi, former director of NIO, and a co-author of the study, adds "remove the last amounts of oxygen, and the Bay of Bengal could become a major global player in nitrogen removal from the oceans". Removing more nitrogen from the oceans could affect the marine nitrogen balance and rates of marine productivity. Globally, warming of the atmosphere through climate change is predicted to lead to an expansion of "dead zones" in the global ocean. It is currently unclear whether climate change would lead to the removal of these last traces of oxygen from the Bay of Bengal waters. However, the Bay of Bengal is also surrounded by a heavy population density, and expected increases in fertilizer input to the Bay may increase its productivity, contributing to oxygen depletion at depth. Bristow warns "Time will tell, but the Bay of Bengal is at a "tipping point", and we currently need models to illuminate how human activities will impact the nitrogen cycle in the Bay of Bengal, and also globally".
Yilmaz S.S.,CBU |
Powder Technology | Year: 2010
In this study, boronizing and/or shot peening surface treatments were applied individually or in combination to the P/M steel specimens. The composition of specimens was 3% Cu. +. 0.2% C. +. balance Fe%. Tensile strength, hardness values and surface properties of treated specimens were determined. Boronizing. +. shot peening surface treatment was found to be the most convenient surface treatment for P/M steel materials based on test results. However, it is important to avoid high peening intensities for shot peening of boronized surfaces because shot peening deteriorates the boronized surface of P/M steel specimens. As a result, surface hardness values such as 1800-2500 HV were achieved after boronizing, the difference between the matrix materials with a hardness of 200 HV was quite high. © 2010 Elsevier B.V.
Ilcik J.,Czech Technical University |
Arora V.,SDU |
Dolejs J.,Czech Technical University
IOP Conference Series: Materials Science and Engineering | Year: 2015
The paper focuses on the updating of the finite element models of the newly developed façade scaffold anchor in the light of the experimental results. The experiments (force-displacement curves) have been carried out on the anchor. The façade scaffold anchor overcomes the problems arising in the process of joining them to the façades through the thermal insulation layers. Using the current methods, the wind load cannot be effectively transferred into the façade and scaffolding stability is decreased. Experimental results are presented and the finite element models of the anchor are developed using non-linear beam and solid elements. It has been observed that the predictions of finite element models that is force-displacement curve do not match with the experiment results. Subsequently, the finite element models of the developed anchor have been updated in the light of experimental results by using the parameter-based finite element model updating method. In case of an anchor, modelling of stiffness of the joints and values of the materials are expected to be dominant sources of inaccuracy in the FE model, assuming that the correct geometric parameters are known. After updating joint stiffness of the anchor joints and material properties, the finite element predictions match with experimental results. The outcomes show that there is a good correlation between the updated finite element models and the experimental data. The accuracy of the updated finite element models is demonstrated by overlaying force-displacement curves with the curve from the experiment, it can be concluded that the updated finite element models of the anchor accurately represent reality. © Published under licence by IOP Publishing Ltd.
News Article | February 15, 2017
The aircraft was on a scheduled flight from Kuala Lumpur to Beijing when it disappeared from air traffic controllers’ radar screens. Military radar continued to track the aircraft, which deviated from its planned route and eventually flew south, finally traveling beyond radar range. The aircraft was never seen or heard from again and the 242 people on board are assumed dead. The aircraft has never been found because nobody knows where it landed or crashed. The best guess is that it flew south for seven hours and then ditched in the Indian Ocean, some 1,800 kilometers southwest of Perth, Australia. But an extensive search of the sea surface and seafloor in that area has found nothing. All that raises an important question: have the authorities been looking in the right place? Today, Ian Holland of the Australian Defence Science and Technology Group publishes some of the reasoning that has defined the search area. Holland has been an important member of the team that has analyzed the data relating to the flight. In particular, he has focused on the last known signals sent from the aircraft to an orbiting Inmarsat communications satellite. In the absence of any other information from the plane, investigators have used these signals to determine the search area—but is there any more that can be gleaned from this data? First some background. MH370 was fitted with a satellite data unit capable of relaying voice conversations and routine data transmissions. It sent its information via an Inmarsat satellite that is geostationary over the Indian Ocean. Although the aircraft transmitted no voice communication, the satellite data unit continued to operate, acknowledging two telephone calls from the ground that went unanswered and making several routine broadcasts such as electronic handshakes and the like. At first glance, it’s hard to imagine how these brief data transmissions can provide any information about the aircraft’s location. But Holland and his colleagues have used them to gather a remarkable amount of information. The communications protocol requires a ground station to make contact with the aircraft’s satellite data unit at a specific time and frequency, regardless of where the plane is on the planet. However, the signal takes time to travel from the ground to the aircraft and back again. This time, known as the burst time offset, is determined by the distance the signal has to travel. This distance is straightforward to calculate. It defines a circle centered on the position on the ground directly below the satellite. However, the calculation does not suggest where on this circle the plane might be, and investigators have had to use other clues to narrow down this position. In total, MH370 sent seven signals from its satellite data unit, each defining a slightly different circle. It sent its final signal at 0019 UTC on March 8, 2014, having initiated a log on request just eight seconds earlier. That’s an important clue. Log on requests only occur when the satellite data unit restarts after some kind of shutdown. Investigators have assumed this shutdown occurred when the plane ran out of fuel and the SDU restarted using power from a device called a ram air turbine, which is deployed in an emergency to generate power. If that is correct, the last transmission must have been near the end of the flight. But how near? Could MH370 have glided many tens or hundreds of kilometers before it hit the ocean? If so, this significantly increases the potential search area. Holland says he and colleagues are able to narrow down this area using another line of mathematical investigation. The satellite data unit broadcasts at a specific frequency, but the aircraft’s velocity toward or away from the satellite introduces a Doppler shift that changes this frequency. This is known as the burst frequency offset. So in theory it’s possible that this shift in frequency can indicate the direction of flight at that instant. In practice, this calculation is hard to do and is much tougher than calculating the distance. Holland’s paper today is largely about this calculation. “The Burst Frequency Offset is a more complex measurement which is generally less well understood,” he says. The calculation is tough because of the number of variables that can influence the frequency. The aircraft’s motion is just one of them. The motion of the satellite plays a role, creating a Doppler shift associated with the uplink and downlink between the satellite and ground station. The ground station also attempts to compensate for any Doppler shift by changing the frequency. And the oscillators in the satellite and aircraft transmitters are not perfect. They vary, producing changes in broadcast frequency. Holland and co attempted to understand all these sources of frequency change by analyzing the broadcasts from MH370 during 20 previous flights in the week before it was lost. Holland goes on to show that if the plane was flying level when a call was made to the plane from the ground soon after contact was lost, then the burst frequency offsets suggest it must have been flying south. That’s important. He also shows that Doppler shifts on the final two broadcasts from the plane’s satellite data unit, suggest that it was descending rapidly. “The downwards acceleration over the 8 second interval between these two messages was found to be approximately 0.68g,” says Holland. This is consistent with the plane being out of control and out of fuel. That has important implications for the search area. If the plane was in an uncontrolled descent, it cannot have flown far after the last broadcast of the satellite data unit. And that means the plane must lie somewhere near the arc calculated from the burst timing offset data. “This suggests that 9M-MRO should lie relatively close to the 7th BTO arc,” concludes Holland. But exactly where on this arc isn’t clear. That’s interesting work which Holland is now opening up to outside scrutiny. He clearly sets out many of the assumptions he and his colleagues have had to make in coming to their conclusion. An important question for the community is whether these assumptions are all justified and whether Holland and his team have overlooked anything. In the meantime, the families of the victims are conducting their own search for wreckage associated with the plane. And until new evidence emerges, the search for MH370 will remain suspended. Ref: arxiv.org/abs/1702.02432: The Use of Burst Frequency Offsets in the Search for MH370
Sahin S.,SDU |
Pure and Applied Geophysics | Year: 2014
The attenuation of coda waves in the earth's crust in southwest (SW) Anatolia is estimated by using the coda wave method, which is based on the decrease of coda wave amplitude in time and distance. A total of 159 earthquakes were recorded between 1997 and 2010 by 11 stations belonging to the KOERI array. The coda quality factor Qc is determined from the properties of scattered coda waves in a heterogeneous medium. Firstly, the quality factor Q0 (the value of Qc at 1 Hz.) and its frequency dependency η are determined from this method depending on the attenuation properties of scattered coda waves for frequencies of 1.5, 3.0, 6.0, 8.0, 12 and 20 Hz. Secondly, the attenuation coefficients (δ) are estimated. The shape of the curve is controlled by the scattering and attenuation in the crustal volume sampled by the coda waves. The average Qc values vary from 110 ± 15 to 1,436 ± 202 for the frequencies above. The Q0 and η values vary from 63 ± 7 to 95 ± 10 and from 0.87 ± 0.03 to 1.04 ± 0.09, respectively, for SW Anatolia. In this region, the average coda Q-f relation is described by Qc = (78 ± 9)f 0.98±0.07 and δ = 0.012 km-1. The low Q0 and high η are consistent with a region characterized by high tectonic activity. The Qc values were correlated with the tectonic pattern in SW Anatolia. © 2013 Springer Basel.
Acta Physica Polonica A | Year: 2015
For the adequate shielding of the radiological equipment using X and gamma rays, special materials with high attenuation properties are needed. This objective may be achieved by the use of concrete. Concrete engineers and technologists must take the role of aggregates more seriously, since there are increasing demands of modern concrete mixtures in terms of technological properties and greater economy. Heavyweight concrete contains aggregates that are natural or synthetic. In this study, metal industry waste products such as iron filings and rebar pieces were used to produce heavy concrete. Physical, mechanical and radiation shielding properties of the obtained concrete with barite, aggregates and artificial aggregates were studied. According to test results, the concrete produced with artificial aggregates can provide the desired physical properties. Radiation shielding coefficient was found to be proportional to the density of concrete.
News Article | March 2, 2017
It takes less than 30 hours for a newborn harbour porpoise (Phocoena phocoena) to develop full hearing abilities. This is faster than any other mammals studied. "Hearing is the most important of the senses for a porpoise, both for adults and calves, so it is logical that a newborn calf spends energy on fine tuning and optimizing this sense as fast as possible," says biologist Magnus Wahlberg, University of Southern Denmark. Together with colleagues Lara Delgado-García from SDU and Jakob Højer Kristensen from the research and experience center Fjord&Bælt in Kerteminde, Denmark, he has published a study in Journal of Comparative Physiology A. Mammals are not born with fully developed hearing. It may take weeks, months or years, and land living mammals need the most time. Guinea pigs need weeks. Cats, rabbits, minks, bats and rats need months. And humans may need years. "A newborn porpoise calf needs a good hearing, so that it can maintain contact with its mother and develop echolocation skills," says Jakob Højer Kristensen. The biologists studied the hearing in two newborns (age 1-4 days old) and three adults from the Fjord&Bælt center. The adults were studied for comparison. No difference between newborns and adults The biologists non-invasively measured the auditory brainstem response in the animals, stimuli consisting of clicks centered at 130 kHz, which is the frequency band used for echolocation and communication in this species. "We saw no significant differences in the hearing of the newborn and the adult porpoises, says Lara Delgado-Garcia." The results indicate that hearing is fully developed within a day from birth, which suggests that harbour porpoise neonates have the earliest hearing development in any mammal studied so far. What about other whales? All other studies of mammal hearing have shown that newborns have only limited or sometimes even absent hearing. This is because hearing is not fully developed, but is still being developed after birth. Humans can hear right after birth - and also before birth—but it takes years before the sense is fully developed (humans are generally slow developers). With the new knowledge about porpoise hearing development, the researchers expect that the same phenomenon might be found in other toothed whales. There are ca. 80 different toothed whale species. Information about hearing in porpoises and other toothed whales is crucial both for understanding the sensory development of newborn toothed whales shaped by evolution, as well as for designing efficient protection mechanisms and legislations for species prone to disturbance by anthropogenic noise from windmills, ship traffic, etc. Explore further: Early baleen whales contended for title of ocean's Barry White
News Article | March 2, 2017
All mammals can hear -- but it is not an ability that is fully developed at birth. Some mammals like humans take years to fully develop their hearing abilities, but for a newborn harbour porpoise it takes less than 30 hours. This is the fastest in any studied mammal. It takes less than 30 hours for a newborn harbour porpoise (Phocoena phocoena) to develop full hearing abilities. This is faster than any other mammals studied. Together with colleagues Lara Delgado-García from SDU and Jakob Højer Kristensen from the research and experience center Fjord&Bælt in Kerteminde, Denmark, he has published a study in Journal of Comparative Physiology A. Mammals are not born with fully developed hearing. It may take weeks, months or years, and land living mammals need the most time. Guinea pigs need weeks. Cats, rabbits, minks, bats and rats need months. And humans may need years. The biologists studied the hearing in two newborns (age 1-4 days old) and three adults from the Fjord&Bælt center. The adults were studied for comparison. No difference between newborns and adults The biologists non-invasively measured the auditory brainstem response in the animals, stimuli consisting of clicks centered at 130 kHz, which is the frequency band used for echolocation and communication in this species. The results indicate that hearing is fully developed within a day from birth, which suggests that harbour porpoise neonates have the earliest hearing development in any mammal studied so far. What about other whales? All other studies of mammal hearing have shown that newborns have only limited or sometimes even absent hearing. This is because hearing is not fully developed, but is still being developed after birth. Humans can hear right after birth - and also before birth -- but it takes years before the sense is fully developed (humans are generally slow developers). With the new knowledge about porpoise hearing development, the researchers expect that the same phenomenon might be found in other toothed whales. There are ca. 80 different toothed whale species. Information about hearing in porpoises and other toothed whales is crucial both for understanding the sensory development of newborn toothed whales shaped by evolution, as well as for designing efficient protection mechanisms and legislations for species prone to disturbance by anthropogenic noise from windmills, ship traffic, etc.