3,213 research outputs found
W-band noise radar in short range applications
No full textNoise Radar Technology (NRT) uses noise waveforms (continuous or pulsed) as a radar signal and correlation processing of the returns for their optimal reception. This paper is devoted to some possible applications of NRT in civil field, in particular to millimetre-wave radars, with comparison of the use of Noise W-band radar versus the more classical FM-CW or pulse compression solutions
High Resolution Measurements and Characterization of Urban, Suburban and Country Clutter at X-Band and Related Radar Calibration
No full textAt Tor Vergata University we are working on measurements and phenomenological characterization of urban, suburban and country radar clutter at X-band (3 cm wavelength, range resolution 8 to 10 m, azimuth resolution @ 1 km about 23.5 m) and on the related radar calibration problems. Measurements are “high resolution” when compared to most surveillance radars, and the related applications are in the frame of clutter maps for cognitive radar, drones detection, radar ornithology, and more. After calibration, done using opportunity targets with known radar cross section and a clutter fence, we carry on an analysis and a comparison of land clutter, considering different weather conditions: dry and wet soil, as well as the rare event of snow. Using fixed opportunity targets, such as lamppost and/or a large cylindrical steel tanker, we describe the attenuation effects due to the natural clutter fence (in this case due to cane thicket near to the target position) and its mitigation when the natural fence is gradually removed. Finally, but importantly, we analyze the multipath phenomenon due to reflection/scattering on ground, and propose a procedure to estimate the multipath factor and to correct for it
Latch-up DC triggering and holding characteristics of n-well, twin-tub and epitaxial CMOS technologies
No full textThe dependence of the latch-up susceptibility on layout parameters is studied on four stripe structures made using different CMOS processes: a standard n-well, a twin-tub and twin-tub epitaxial technology. The correlation between triggering currents, well and substrate resistances and parasitic transistor gains is studied by means of emitter current triggering measurements and two-dimensional simulations using HFIELDS. Triggering currents higher than 250 mA are obtained on epitaxial structures with n+ guard-rings. Anomalies in triggering and holding electrical characteristics are caused by the three-dimensional distribution of the latch-up current, which is observed by IR microscopy. These anomalies can affect results of conventional latch-up testing method
The importance of breeding vocalizations for mate attraction in a freshwater goby with composite sound repertoire.
No full textMale gobies, Padogobius martensii, emit 'tonal' sounds during courtship, and 'drumming' and 'complex' sounds during spawning. The complex sound is a two-part vocalization consisting of a drumming sound followed without pause by a tonal sound. In the laboratory, the playback of both the tonal sound and the drumming sound to ripe females P. martensii determined oriented approaching and increased the time spent by the subject within the loudspeaker area. Response levels to the sound playback (drumming sounds) tended to be correlated with degree of ripeness of the female. Functional aspects of the female response to both types of acoustic stimuli are discussed
Effect of Concentration on the Supramolecular Polymerization Mechanism via Implicit-Solvent Coarse-Grained Simulations of Water-Soluble 1,3,5-Benzenetricarboxamide
No full textWe report an implicit-solvent coarse-grained (CG) model for a water-soluble 1,3,5-benzenetricarboxamide (BTA) supramolecular polymer. The technical advances guaranteed by this CG model allow simulation of the self-assembly of 1000 BTA monomers and easy variation of the BTA concentration into the system down to experimental dilute conditions. In this way, we can monitor the mechanism of supramolecular polymerization as a function of the concentration at submolecular resolution exceeding the microsecond time scale. While increasing the concentration produces rapid formation of large disordered clusters that are then converted into BTA fibers, moving to very dilute concentrations favors early ordering of the oligomers in solution even at small sizes. Interestingly, we observe that below a certain concentration the oligomers that dynamically grow in solution during the self-assembly present the same level (and amplification) of order of prestacked equilibrated oligomers of the same size, meaning that concentration-dependent kinetic effects have disappeared from the polymerization mechanism
Molecular modelling of supramolecular polymers
No full textNature uses self-assembly for building supramolecular materials possessing fascinating properties (self-healing, adaptive, reconfigurable and responsive) that are fundamental for many complex biological functions. Artificial supramolecular polymers, composed of monomers that self-assemble via non-covalent interactions, are attracting increasing interest as platforms for building innovative materials, as these possess similar bioinspired dynamic properties. However, their design still relies on an inefficient/expensive trial-and-error approach. A key question is how to design the monomers to control the properties of the supramolecular polymer. Most often, obtaining from the experiments molecular-level information on how to control these assemblies is prohibitively difficult. Molecular modelling is a fundamental support in this field, allowing investigation of the supramolecular polymer from a privileged point of view and at high-resolution. Such a ‘virtual microscope’ can provide information on the factors that control supramolecular polymer structure and dynamics, on the monomer–monomer interactions and their cooperativity that are precluded to the experiments, paving the way to structure–property relationships useful to advance the rational design of such materials. This review discusses the state of the art of molecular modelling and simulation of supramolecular polymers. The field is advancing quickly. But the detailed insight that can be reached and the continuous technical developments promise that this is only the beginning
Waveforms design for modern and MIMO radar
No full textOne of the main focus of the research in modern
radar systems, as MIMO (Multiple Input Multiple Output) radar
and multifunction/multistatic radar, is the waveforms design and
optimization in order to get a low degradation in the main lobe
(low Signal to Noise Ratio loss), a low Peak Side-Lobe Ratio
(PSLR) and good orthogonality properties. In MIMO
applications typically M different waveforms, or codes, are
required, where M is the number of the transmit elements. In
reception the orthogonal property of the M transmitted
waveforms permits their separation. Orthogonality may be
imposed in time domain, in frequency domain or in signals space.
In most radar applications, obtaining the orthogonality in the
signals domain is the best choice. Good candidates to design
deterministic signals that satisfy the orthogonality requirements
are the well-known “up” and “down” chirp (Linear-FM and
Non-LFM), the Costas codes, the Alltop sequences and the
OFDM signals. Another important class of orthogonal signals are
the random signals such as the noise waveforms. In this paper we
present the main characteristics of these signals and their
comparison through a characterization, including an analysis of
the auto and cross correlation functions, and of the spectral
properties, with recommendations for practical use
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