70 research outputs found
On optimum gain of onboard jammer antennas
No full textThe radar cross section (RCS) of a modern low-detectable aircraft with onboard self-screening jammers is determined greatly by the RCS of the jammer antenna. The increase of the antenna gain results, not only, in a higher jammer erp, but also, in an increase in the radar detectability of the aircraft due to the increase of the contribution of the RCS of the antenna to the total RCS of the aircraft. This basic problem of onboard self-screening jammers is discussed in this paper and formulas of the optimum on-board jammer antenna gain and its relative effectiveness are presented. The effect of the jammer antenna gain on jamming effectiveness is illustrated and representative results are reported
Reduced-size dual band Wilkinson power dividers
No full textIn this paper, two new shaped dual band Wilkinson power dividers are presented. These configurations achieve significant size reduction and very good performance as compared to the conventional dual band Wilkinson power divider. Simulation and experimental results of two reduced size dividers at the receiving bands of the Global system for mobile communication GSM demonstrate the realizablity and performance of the proposed configurations. The implementation of the proposed structures on GaAs (Gallium Arsenide) for X-band and Ku-band satellite down-link bands yields miniature configurations appropriate for MIC/MMIC applications. ©2008 IEEE.IEE
Compact Bandstop Filters with Extended Upper Passbands
No full textThis paper presents new compact bandstop filters (BSFs) with extended upper passbands. In the basic proposed filter configuration, the conventional quarter-wavelength open-stub resonators are replaced with equivalent two-section stepped impedance resonators. Transmission line analysis is used to determine the dimensions of the equivalent stepped impedance sections. The filter structure is analyzed using a full wave electromagnetic (EM) simulator and then realized at 2.3GHz band. Experiments have also been done to validate the performance of the design concept. Compared with the conventional quarter-wavelength-based bandstop filter, significant extensions of the upper passband beyond 9GHz and 40% size reduction are achieved. Two other variations of the proposed basic BSF with further size reduction (more than 60%) are implemented and their measured performances are verified
Harmonic suppressed and size-Reduced bandstop and bandpass filters
No full textNew bandstop/bandpass microstrip structures with harmonic suppression are presented in this article. By replacing the series quarter-wavelength connecting lines of conventional open-stub bandpass/bandstop filters with the equivalent II-shaped line section, compact open-stub bandstop/bandpass filters with second harmonic suppression are achieved. Transmission-line theory is used to derive the design equations of the equivalent II-shaped lines. Simulation and experiments have also been done to validate the proposed design concept. When compared with the conventional open-stub Bandpass/Bandstop filters, the second harmonic is suppressed and size reduction is achieved in both the Bandstop/bandpass structures. Moreover, results confirm that the proposed shaped bandpass filter achieves a further third harmonic rejection. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2109-2114, 2009 Published online in Wiley InterScience (www.interscience.wiley.com)
Creating a Front Door to Archival Knowledge in the United States: Guidelines for a Master of Archival Studies Degree
No full textThe author explores the need for the Master of Archival Studies (M.A.S.) degree in the United States and its expression through the Society of American Archivists' Guidelines for the Development of a Curriculum for a Master of Archival Studies. He contends that the substantial and distinct body of archival knowledge, coupled with the emergence of new information technologies that have changed the way archives are created, maintained, and used, make an autonomous two-year degree curriculum necessary. The article examines SAA's history in educational guidelines development, the Canadian experience with educational guidelines and twelve years of M.A.S. degree programs, the growth of U.S. graduate archival education during the 1980s, and major features of the 1993 draft M.A.S. guidelinesThis article is from Archival Issues 18 (1993): 77–95.</p
Automatically Testing a Conversational Crowd Computing Platform
No full textThe rise in the use of crowd computing platforms led to the birth of Dandelion, a conversational crowd computing platform developed at TU Delft with the main goals being to connect students with researchers and to allow students to report on their well-being by using a friendly interface. Dandelion was tested manually up to the time of drafting this paper; thus, the primary motivation behind this paper is to ensure the robustness and measure the responsiveness of Dandelion.Robustness was exercised by utilizing a simulated user behaving unexpectedly. The testing framework then classifies the behaviour of Dandelion according to the C.R.A.S.H. scale. The testing framework is validated by altering Dandelion's behaviour and ensuring that the test results reflect the change. Furthermore, a lower bound to the run time of a task will be estimated using a Multi-Agent System (M.A.S.) simulation on Dandelion.Upon verifying the correctness of the robustness test, a faulty assumption was uncovered on which the user's input validation was based. Furthermore, the M.A.S. simulation run estimated a lower bound of seconds, while revealing a lack of user's input validation before posting them in the database.CSE3000 Research ProjectComputer Science and Engineerin
Lens Antenna for Wide Angle Beam Scanning at 79 GHz for Automotive Short Range Radar Applications
No full textInternational audienceThis communication presents the design and experimental verification of a substrate integrated waveguide fed lens antenna for 79 GHz automotive radar applications. The proposed integrated lens antenna consists of a six layer cylindrical Luneburg lens illuminated by 17 source elements of substrate integrated waveguide fed by a planar log periodic dipole antenna array. The Luneburg lens is developed by using a unique foam material AirexR82 (r = 1.12), which is drilled and pressed to achieve the different dielectric constant needed to follow the index law inside the lens. The return loss and the radiation characteristics of the proposed integrated lens antenna are investigated and validated by measurements. A good agreement between the measured and simulated results is observed. The measured results confirm the beam scanning capability of the proposed integrated lens antenna for a wide scan angle of ±85° in azimuth plane having a maximum antenna gain of 15 dBi at 82.5 GHz and gain drop of less than 2.75 dB for the edge feeds. The estimated radiation efficiency of the antenna is found to be 67% at 82.5 GHz. © 1963-2012 IEEE
Mixed Bruce-Roberts numbers
No full text[EN] We extend the notions of mu*- sequences and Tjurina numbers of functions to the framework of Bruce-Roberts numbers, that is, to pairs formed by the germ at 0 of a complex analytic variety X. Cn and a finitely R( X)-determined analytic function germ f : (Cn, 0). (C, 0). We analyze some fundamental properties of these numbers.Part of this work was developed during the stay of the first author at the Departamento de Matematica of ICMC, Sao Carlos, Universidade de Sao Paulo (Brazil), in February and July 2018. The first author wishes to thank this institution for their hospitality and working conditions and to FAPESP for financial support. The first author was partially supported by MICINN Grant PGC2018-094889-B-I00 and FAPESP Grant 2014/00304-2. The second author was partially supported by CNPq Grant 306306/2015-8 and FAPESP Grant 2014/00304-2.Bivià-Ausina, C.; Ruas, M. (2020). Mixed Bruce-Roberts numbers. Proceedings of the Edinburgh Mathematical Society. 63(2):456-474. https://doi.org/10.1017/S0013091519000543S456474632Damon, J. (1996). Higher multiplicities and almost free divisors and complete intersections. Memoirs of the American Mathematical Society, 123(589), 0-0. doi:10.1090/memo/0589Wahl, J. M. (1983). Derivations, automorphisms and deformations of quasihomogeneous singularities. Proceedings of Symposia in Pure Mathematics, 613-624. doi:10.1090/pspum/040.2/713285De Goes Grulha, N. (2008). THE EULER OBSTRUCTION AND BRUCE-ROBERTS’ MILNOR NUMBER. The Quarterly Journal of Mathematics, 60(3), 291-302. doi:10.1093/qmath/han011Greuel, G.-M. (1975). Der Gau�-Manin-Zusammenhang isolierter Singularit�ten von vollst�ndigen Durchschnitten. Mathematische Annalen, 214(3), 235-266. doi:10.1007/bf01352108Gaffney, T. (1996). Multiplicities and equisingularity of ICIS germs. Inventiones Mathematicae, 123(1), 209-220. doi:10.1007/bf01232372Damon, J. (2002). On the freeness of equisingular deformations of plane curve singularities. Topology and its Applications, 118(1-2), 31-43. doi:10.1016/s0166-8641(01)00040-2Bruce, J. W., & Roberts, R. M. (1988). Critical points of functions on analytic varieties. Topology, 27(1), 57-90. doi:10.1016/0040-9383(88)90007-9Decker, W. , Greuel, G.-M. , Pfister, G. and Schönemann, H. , Singular 4-0-2. A computer algebra system for polynomial computations. Available at http://www.singular.uni-kl.de (2015).Looijenga, E. J. N. (1984). Isolated Singular Points on Complete Intersections. doi:10.1017/cbo9780511662720AHMED, I., RUAS, M. A. S., & TOMAZELLA, J. N. (2013). Invariants of topological relative right equivalences. Mathematical Proceedings of the Cambridge Philosophical Society, 155(2), 307-315. doi:10.1017/s0305004113000297Aleksandrov, A. G. (1986). COHOMOLOGY OF A QUASIHOMOGENEOUS COMPLETE INTERSECTION. Mathematics of the USSR-Izvestiya, 26(3), 437-477. doi:10.1070/im1986v026n03abeh001155Briançon, J., & Maynadier-Gervais, H. (2002). Sur le nombre de Milnor d’une singularité semi-quasi-homogène. Comptes Rendus Mathematique, 334(4), 317-320. doi:10.1016/s1631-073x(02)02256-2Giusti, M., & Henry, J.-P.-G. (1980). Minorations de nombres de Milnor. Bulletin de la Société mathématique de France, 79, 17-45. doi:10.24033/bsmf.1907Hauser, H., & Müller, G. (1993). Affine varieties and lie algebras of vector fields. Manuscripta Mathematica, 80(1), 309-337. doi:10.1007/bf03026556Liu, Y. (2018). Milnor and Tjurina numbers for a hypersurface germ with isolated singularity. Comptes Rendus Mathematique, 356(9), 963-966. doi:10.1016/j.crma.2018.07.004Nuno-Ballesteros, J. J., Orefice, B., & Tomazella, J. N. (2011). THE BRUCE-ROBERTS NUMBER OF A FUNCTION ON A WEIGHTED HOMOGENEOUS HYPERSURFACE. The Quarterly Journal of Mathematics, 64(1), 269-280. doi:10.1093/qmath/har032Ohmoto, T., Suwa, T., & Yokura, S. (1997). A remark on the Chern classes of local complete intersections. Proceedings of the Japan Academy, Series A, Mathematical Sciences, 73(5), 93-95. doi:10.3792/pjaa.73.93Lê Tráng, D. (1974). Calculation of Milnor number of isolated singularity of complete intersection. Functional Analysis and Its Applications, 8(2), 127-131. doi:10.1007/bf0107859
Astrometric satellite Hipparcos: gridstep-inconsistency correction during reduction on circles
No full text"Hipparcos” is the name of an astrometric satellite under development by the European Space Agency. Hipparcos is an acronym for High Precision Parallax Collecting Satellite. The aim of the Hipparcos project is to determine astrometric parameters of about 100,000 selected stars. These parameters consists of parallaxes, positions, proper motions. Hipparcos will gather other information too, like magnitudes and colour indices. The expected average accuracy is a 2 m.a.s. (milli arc second) standard deviation in position, anual proper motion and parallax. To gather the information needed to determine these astrometric parameters with such a precision, the satellite is equipped with a telescope. This telescope has two fields of view, separated by an angle of approximately 58 degrees, called the "basic angle”. The satellite is rotating, so the two fields of view of about 1 by 1 degree scan the whole sky. The light, received from the stars passing the fields of view, is modulated by a grid. Behind the grid, photons are counted during short periods of time. In this way some 100 billion photon count measurements will be registered during the 2.5 year mission.Civil Engineering and Geoscience
Integrated lens antenna array with full azimuth plane beam scanning capability at 60 GHz
No full textInternational audienceAn antenna array operating at 60 GHz is proposed. The proposed array covers impedance bandwidth of 5 GHz (57.5–62.5 GHz) with maximum gain of 16.25 dBi at 61. 5 GHz. With the proposed array 15 distinct radiation patterns in azimuth plane can be achieved, each having 3-dB beamwidth of 24° and 3-dB cross over. The beam scanning capability can be achieved by activating each array element one by one. Each array element consists of a conventional microstrip patch antenna (MPA) integrated with extended hemispherical Teflon lens. The Teflon lens is utilized to enhance the gain of conventional MPA as well as to achieve the desired elementary radiation pattern of array to cover full azimuth plane. A very good agreement between the measured and simulated results is observed. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:116–120, 2017. © 2016 Wiley Periodicals, Inc
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