Frederick Research Center

Frederick, United States

Frederick Research Center

Frederick, United States

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Wijaya D.D.,Bandung Institute of Technology | Haralambous H.,Frederick University | Oikonomou C.,Frederick Research Center | Kuntjoro W.,Bandung Institute of Technology
Journal of Geodesy | Year: 2017

The critical frequency of ionospheric F2 layer (foF2) is a measure of the highest frequency of radio signal that may be reflected back by the F2 layer, and it is associated with ionospheric peak electron density in the F2 layer. Accurate long-term foF2 variations are usually derived from ionosonde observations. In this paper, we propose a new method to observe foF2 using a stand-alone global positioning system (GPS) receiver. The proposed method relies on the mathematical equation that relates foF2 to GPS observations. The equation is then implemented in the Kalman filter algorithm to estimate foF2 at every epoch of the observation (30-s rate). Unlike existing methods, the proposed method does not require any additional information from ionosonde observations and does not require any network of GPS receivers. It only requires as inputs the ionospheric scale height and the modeled plasmaspheric electron content, which practically can be derived from any existing ionospheric/plasmaspheric model. We applied the proposed method to estimate long-term variations of foF2 at three GPS stations located at the northern hemisphere (NICO, Cyprus), the southern hemisphere (STR1, Australia) and the south pole (SYOG, Antarctic). To assess the performance of the proposed method, we then compared the results against those derived by ionosonde observations and the International Reference Ionosphere (IRI) 2012 model. We found that, during the period of high solar activity (2011–2012), the values of absolute mean bias between foF2 derived by the proposed method and ionosonde observations are in the range of 0.2–0.5 MHz, while those during the period of low solar activity (2009–2010) are in the range of 0.05–0.15 MHz. Furthermore, the root-mean-square-error (RMSE) values during high and low solar activities are in the range of 0.8–0.9 MHz and of 0.6–0.7 MHz, respectively. We also noticed that the values of absolute mean bias and RMSE between foF2 derived by the proposed method and the IRI-2012 model are slightly larger than those between the proposed method and ionosonde observations. These results demonstrate that the proposed method can estimate foF2 with a comparable accuracy. Since the proposed method can estimate foF2 at every epoch of the observation, it therefore has promising applications for investigating various scales (from small to large) of foF2 irregularities. © 2017 Springer-Verlag Berlin Heidelberg


Grant
Agency: European Commission | Branch: FP7 | Program: CP-FP | Phase: AAT.2010.1.1-2.;AAT.2010.4.1-5. | Award Amount: 7.06M | Year: 2011

The concept of the MERLIN project is to reduce the environmental impact of air transport using Additive Manufacturing (AM) techniques in the manufacture of civil aero engines. MERLIN will develop AM techniques, at the level 1 stage, to allow environmental benefits including near 100% material utilisation, current buy to fly ratios result in massive amounts of waste, no toxic chemical usage and no tooling costs, to impact the manufacture of future aero engine components. All of these factors will drastically reduce emissions across the life-cycle of the parts. There will also be added in-service benefits because of the design freedom in AM. Light-weighting, and the performance improvement of parts will result in reduced fuel consumption and reduced emissions. MERLIN will seek to develop the state-of-the-art by producing higher performance additive manufactured parts in a more productive, consistent, measurable, environmentally friendly and cost effective way. The MERLIN consortia has identified the following areas where a progression of the state-of-the art is needed to take advantage of AM: Productivity increase. Design or Topology optimisation. Powder recycling validation. In-process NDT development. In-process geometrical validation. High specification materials process development. The MERLIN consortium comprises six world leading aero engine manufacturers, Rolls-Royce is the coordinator, six renowned RTD providers and two intelligent SMEs. Impacts will include the development of high value, disruptive AM technologies capable of step changes in performance which will safeguard EU companies in the high value aero engine manufacturing field. AM will significantly reduce waste in an industry where materials require massive amounts of energy and toxic chemicals, in-process toxic chemical usage will be massively reduced, and emissions will drop because of the reduced amount of material involved.


Nikolaou S.,Frederick Research Center | Davidovic M.,Frederick Research Center | Davidovic M.,University of Belgrade | Nikolic M.,University of Belgrade | Vryonides P.,Frederick University
Proceedings of the 5th European Conference on Antennas and Propagation, EUCAP 2011 | Year: 2011

In this paper three types of resonators are considered as a notch creating resonator for a UWB rectangular monopole. The three types of resonators are: a slot ring resonator (SRR), a U-shaped slot and a capacitively loaded loop (CLL) resonator. These notch creating resonators, are positioned on three different areas of the antenna, the ground plane, the feed line and the rectangular radiator, and the different cases are compared using simulated return loss and radiation pattern plots. Additionally the potential integration of p-i-n dioded switches for the creation of a potentially reconfigurable frequency notch is investigated. The contacted research suggests that, the use of CLL resonator has a number of advantages that makes CLL resonator an attractive choice for reconfigurable frequency notch UWB antenna designs. © 2011 EurAAP.


Lakafosis V.,Georgia Institute of Technology | Rida A.,Georgia Institute of Technology | Vyas R.,Georgia Institute of Technology | Yang L.,Texas Instruments | And 2 more authors.
Proceedings of the IEEE | Year: 2010

This paper discusses the evolution towards the first integrated radio-frequency identification (RFID)-enabled wireless sensor network infrastructure using ultra-high frequency/radio frequency (UHF/RF) RFID-enabled sensor nodes and inkjet-printed electronics technologies on flexible and paper substrates for the first time ever. The first sections highlight the unique capabilities of inkjet printed electronics as well as the benefits of using paper as the ultra-low-cost, conformal and environmentally friendly substrate for the mass-scale ubiquitous implementation of the first RFID-enabled wireless sensing applications. Various inkjet-printed antenna configurations are presented for enhanced-range compact RFID-enabled sensing platforms in rugged environments up to 7 GHz, followed by the discussion of their 2-D integration with integrated circuit (IC) and sensors on paper. This integration is extended to a power-scavenging smart-shoe batteryless integrated RFID module on paper that could be used for autonomous wearable sensing applications with enhanced range. The paper concludes discussing the details for establishing for the first time an asynchronous wireless link between the aforementioned RFID-tags and a widely used commercial wireless sensor network (WSN) mote using a simplified protocol; a paramount step that could potentially create ubiquitous ultra-low-cost sensor networks and large-scale RFID implementations eliminating the need of expensive RFID reader infrastructure and linking RFIDs to the mature level of WSNs. © 2006 IEEE.


Haralambous H.,Frederick University | Oikonomou C.,Frederick Research Center
Advances in Space Research | Year: 2015

We investigate first the climatology expressed by diurnal and seasonal variations of the critical frequency (foF2) and the peak height (hmF2) of the F2-layer derived from digital ionosonde measurements at the low-middle latitude European station in Nicosia, Cyprus (geographical coordinates: 35°N, 33°E, geomagnetic lat. 29.38°N, I = 51.7°). Monthly median hourly values of the F2-layer peak characteristics are obtained using manually scaled data during the 5-year period 2009-2013. The observational results are then compared with the International Reference Ionospheric Model (IRI-2012) predictions using both URSI and CCIR coefficients. It is shown that the semi-annual pattern of daytime foF2 characterized by higher values at equinoxes than either solstices as well as the winter anomaly phenomenon demonstrate strong solar activity dependence. An annual pattern of night-time foF2 is also detected with lower values in winter and higher in summer. The seasonal variation of daytime hmF2 is evident and peaks of hmF2 at pre-sunrise and post-sunset hours are identified during December. The IRI-2012 model is capable to capture the main diurnal and seasonal patterns of foF2 and hmF2. The highest overestimation of daytime foF2 is noted at equinoxes and solstices except from March, October, December of 2011, and June of 2013. Significant foF2 underestimation is observed at evening and after midnight during February and March of 2009. Large positive discrepancies between the modeled and observed hmF2 values are noticed during the deep solar minimum year 2009. Overall, IRI-model estimates are more accurate for hmF2 than foF2 over Cyprus and for the examined period. © 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.


Papadopoulos H.,Frederick University | Papadopoulos H.,Frederick Research Center
Neurocomputing | Year: 2013

Venn Prediction (VP) is a new machine learning framework for producing well-calibrated probabilistic predictions. In particular it provides well-calibrated lower and upper bounds for the conditional probability of an example belonging to each possible class of the problem at hand. This paper proposes five VP methods based on Neural Networks (NNs), which is one of the most widely used machine learning techniques. The proposed methods are evaluated experimentally on four benchmark datasets and the obtained results demonstrate the empirical well-calibratedness of their outputs and their superiority over the outputs of the traditional NN classifier. © 2012 Elsevier B.V.


Chrysostomou C.,Frederick University | Tatas K.,Frederick Research Center | Runcan A.R.,Frederick University
Proceedings - 15th IEEE International Conference on Computational Science and Engineering, CSE 2012 and 10th IEEE/IFIP International Conference on Embedded and Ubiquitous Computing, EUC 2012 | Year: 2012

This paper proposes a novel, adaptive routing scheme for Network-on-Chip (NoC). In particular, the proposed routing scheme decides on the output port of an incoming flit by taking into account the dynamic traffic and power consumption on neighboring router links. For that, a simple, generic, and efficient nonlinear control law is built, based on fuzzy logic control, to dynamically calculate the input links cost. Although we focus on bufferless NoCs, it can also be applied to buffered NoCs as well. The additional digital logic required for the proposed scheme is not in the router critical path, and, therefore, imposes no additional latency. We demonstrate, via simulative evaluation of light to heavy congestion conditions, that the proposed scheme outperforms representative conventional counterparts in terms of throughput and latency. Thus, the effectiveness of the proposed scheme is shown, as the performance is consistently better. © 2012 IEEE.


Oikonomou C.,Frederick Research Center | Haralambous H.,Frederick Research Center | Haldoupis C.,University of Crete | Meek C.,University of Saskatchewan
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2014

In this study, ionogram observations made with the Cyprus digisonde (35°N; 33°E) are analyzed by applying an ionosonde height-time-intensity (HTI) methodology. The aim is to study dominant periodicities and diurnal patterns in occurrence and altitude transport of sporadic E (Es) and intermediate descending layers (IDL), which are impacted upon by solar thermospheric tides via the windshear layer formation mechanism in the E and lower F region ionosphere. The results show the diurnal occurrence and altitude descent of sporadic E to be dominated by a semidiurnal tide-like periodicity, which prevails, with some differences, in all seasons. It is characterized by a daytime layer starting near sunrise at ~125. km, followed by a nighttime layer appearing first in late afternoon at ~130. km; both layers descend in altitude with speeds between about 2 and 3. km/h, therefore reaching the 100. km level in ~10-12. h. Also, a terdiurnal tide-like periodicity is present in daily Es occurrence and altitude descent but only in summer solstice. In addition, the data show fast-descending layers to originate at F region altitudes near sunrise and sunset, which are subject to a semidiurnal periodicity. Although these layers are rarely seen by the digisonde below about 180. km for most times and never during the night, the data hint that they connect with sporadic E layers below, therefore, both IDLs and Es form an integral tidal ion layer system in the lower ionosphere. An exceptional result is the detection during daytime of strong intermediate descending layers in March equinox, starting at F region and descending downwards with speeds of ~10. km/h. Although an effort is made to interpret this equinoctial IDL signature, more work is needed for its understanding. © 2014 Elsevier Ltd.


Haralambous H.,Frederick Research Center | Oikonomou C.,Frederick Research Center
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2013

The determination of the ionospheric electron density profile below the electron density peak (bottomside) has been traditionally conducted by ground-based ionosondes, which probe the ionosphere up to the maximum electron density and define the profile above the peak (topside) using functions which extrapolate the profile above the peak. An alternative modern technique for measuring electron density profiles is the GPS Radio Occultation, conducted by means of signals transmitted by GPS satellites and received by LEO satellites. The FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) is such a system operating since 2006. In this paper a comparison of the topside electron density profiles over Cyprus is investigated in terms of these two different measurement techniques, within a period of four years. The ability of the International Reference Ionosphere model (IRI-2012) to represent the topside electron density profile is also examined. © 2013 IEEE.


Haralambous H.,Frederick Research Center
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2013

Sporadic E layer is an ionospheric phenomenon which has been classified as an E region (90-150 km) irregularity described by thin layers of extremely dense ionization patches which can significantly affect radio wave propagation. Especially in the case of Cyprus complete blocking of HF signals emanating from short and long-distance HF signals has been observed around noon during the summer. Sporadic E layer can occur during daytime or night-time, and its characteristics vary with latitude. The generating mechanism of the phenomenon has been explained within the general concept of neutral atmosphere-ionosphere coupling and in accordance to windshear theory where long-lived metal ions in the lower thermosphere move vertically to converge into dense plasma layers under the combined action of ion-neutral collisional coupling and geomagnetic Lorentz forcing driven by vertical shears in the horizontal wind. Sporadic E layer formation has been correlated in literature with solar activity, geomagnetic activity and associated to thunderstorms and meteor showers. © 2013 IEEE.

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