Teodor Petrescu

An experimental evaluation of 3D mesh decimation techniques

Recent trends in computer graphics has lead to a spectacular grow of the amount of complex 3D objects stored and exchanged over the Internet. In this context accurate mesh decimations schemes are becoming more and more urgent due to the rendering speed reason and fast transmission. In this paper we present a complete evaluation of the mesh simplification techniques existing in the technical literature. After a short survey and characterization of the local and global simplification schemes we retained only the most efficient algorithms for a further analysis. In order to obtain a competitive evaluation, two different metrics were considered: Hausdorff and mean geometric error, which determine the deviance between the original model and the simplified version of it. We compared the approximation accuracy for each technique and established the optimal method in terms of decimation rates and precision.

Backward couplers using coupled composite right/left-handed transmission lines

A new asymmetric backward coupler is obtained by edge-coupling two types of composite right/left handed (CRLH) lines. This novel coupler is analyzed in a microwave range (1–10 GHz) and the magnitude of the scattering parameters reveals tight coupling effects (even 0 dB) in a dual frequency band and also very good directivity in the working band.

Time-domain pulse-matched synthesis of ultra-wide band antennas

Antenna synthesis can yield optimal radiating structures in terms of pattern diagram, gain, bandwidth or other figures of merit. Although the synthesis might be more difficult for continuous sources than for antenna arrays the resulting radiating structures are cheaper and easy to manufacture. In this paper, we propose a time-domain synthesis approach for ultra-wide band antennas. The method is based on a finite expansion of the antenna time-domain response. The synthesis is performed with regard to the resemblance between the time-domain radiated waveform and the waveform at the antenna input. The approach is validated by synthesizing a planar, ultra-wide band antenna designed for a particular waveform of excitation.

Propagation effects on radio signals emitted in salt by neutrino-induced electromagnetic showers

We are investigating the possibility to reconstruct the energy and direction of cosmic neutrinos from the measured voltage of the radio signals emitted. The detector based on the Askaryan effect is built in salt so all propagation effects that affect the characteristics of the generated radio signal should be characterized. Measurements are also influenced by the properties of antenna so its behavior is briefly discussed. We have considered that limitations in resolution of the electronic system is given by ADC and presented its influence on the recovery of direction of the incoming neutrino.

Multiresolution median filtering based video temporal segmentation

In this paper we introduce an enhanced graph partition model, more robust, used for video sequences temporal segmentation. In the first part we examine the formal framework of the shot boundary detection techniques implemented in the recent years, emphasizing the weakness and strength for each method. In the second phase we present our novel algorithm that applies a scale space median filtering on a min-max objective function that optimize the association within each graph cut in order to remove noise caused by camera movement or large object displacement. The algorithm evaluation is done on a subset of movies from the TRECVID 2001 and 2002 video database which demonstrate the improved performance of our method regardless to the noise gender, with precision and recall rates of average 90% and 86 %, respectively. In the end we conclude the paper and present some further implementation.

On the accuracy of the distance-averaging method for antenna gain measurements

We have previously proposed an indoor measuring technique for antenna gain, based on averaging a normalized transfer function over a distance range. Simulated and measured results have also been presented, in order to validate the method. In this paper, we assess the accuracy of our method by comparing the results to those issued from a traditional, non-anechoic approach, i.e., the time-gating method, as well as from measurements inside an anechoic chamber. A good agreement between the results issued from the three techniques was noted. Further, it appears that measurements in the intermediate-field region are also possible with the distance averaging method.

On some implementation issues for time-domain, pulse-matched synthesized antennas

Low-distortion antennas for pulsed excitation can be synthesized by using a technique based on a finite expansion of the antenna time-domain response. Current profiles can therefore be generated in order to achieve optimal response for a given waveform of excitation. However, the simplest radiating structures resulting from synthesis might neither provide acceptable input matching, nor omnidirectional radiation. This paper addresses these two issues and further proposes two antenna structures.

Autonomous robotic platforms for locating radio sources buried under rubble

This paper deals with the use of autonomous robotic platforms able to locate radio signal sources such as mobile phones, buried under collapsed buildings as a result of earthquakes, natural disasters, terrorism, war, etc. This technique relies on averaging position data resulting from a propagation model implemented on the platform and the data acquired by robotic platforms at the disaster site. That allows us to calculate the approximate position of radio sources buried under the rubble. Based on measurements, a radio map of the disaster site is made, very useful for locating victims and for guiding specific rubble lifting machinery, by assuming that there is a victim next to a mobile device detected by the robotic platform; by knowing the approximate position, the lifting machinery does not risk to further hurt the victims. Moreover, by knowing the positions of the victims, the reaction time is decreased, and the chances of survival for the victims buried under the rubble, are obviously increased.

Propagation models for non line-of-sight scenarios

The log-normal propagation model is usually applied for scenarios including a line-of-sight path. However, there are many cases that do not include such a propagation path, e.g. indoor transmission and disaster situations, when radio waves have to penetrate trough ruins. In this paper, we show that the log-normal model can also be applied for non line-of-sight transmission. Both indoor scenario and trough-ruins scenario, are investigated.

A synthesis approach for antennas with a quasi-linear gain variation over a wide frequency range

In this paper, we propose to extend the frequency-domain synthesis approach based on a variable slope profile for antennas with a linear variation over a fractional bandwidth in the order of 100%. In that case the inflection point on the resulting profile is no longer located at its half. Thus, the profile shape will no longer be folded at the half, but at a coordinate closer to the end, the resulting shape approaching to a bow-tie antenna than to a circular dipole antenna.