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Volker Durr - One of the best experts on this subject based on the ideXlab platform.

  • comparative whole body kinematics of closely related insect species with different body morphology
    The Journal of Experimental Biology, 2015
    Co-Authors: Leslie Theunissen, Holger Bekemeier, Volker Durr
    Abstract:

    Legged locomotion through natural environments is very complex and variable. For example, leg kinematics may differ strongly between species, but even within the same species it is adaptive and context-dependent. Inter-species differences in locomotion are often difficult to interpret, because both morphological and ecological differences among species may be strong and, as a consequence, confound each other's effects. In order to understand better how body morphology affects legged locomotion, we compare unrestrained whole-body kinematics of three stick insect species with different body proportions, but similar feeding ecology: Carausius morosus, Aretaon asperrimus and Medauroidea extradentata (= Cuniculina impigra ). In order to co-vary locomotory context, we introduced a gradually increasing demand for climbing by varying the height of stairs in the setup. The species were similar in many aspects, for example in using distinct classes of steps, with minor differences concerning the spread of corrective short steps. Major differences were related to Antenna Length, segment Lengths of thorax and head, and the ratio of leg Length to body Length. Whereas all species continuously moved their Antennae, only Medauroidea executed high swing movements with its front legs to search for obstacles in the near-range environment. Although all species adjusted their body inclination, the range in which body segments moved differed considerably, with longer thorax segments tending to be moved more. Finally, leg posture, time courses of leg joint angles and intra-leg coordination differed most strongly in long-legged Medauroidea .

Bert Hecht - One of the best experts on this subject based on the ideXlab platform.

  • impedance matching and emission properties of nanoAntennas in an optical nanocircuit
    Nano Letters, 2009
    Co-Authors: Jershing Huang, Thorsten Feichtner, Paolo Biagioni, Bert Hecht
    Abstract:

    An experimentally realizable prototype optical nanocircuit consisting of a receiving and an emitting nanoAntenna connected by a two-wire optical transmission line is studied using finite-difference time- and frequency-domain simulations. To optimize the coupling between optical nanocircuit elements we apply impedance matching concepts in analogy to radio frequency technology. We show that the degree of impedance matching, and in particular the impedance of the emitting nanoAntenna, can be inferred from the experimentally accessible standing wave pattern on the transmission line. We demonstrate the possibility of matching the nanoAntenna impedance to the transmission line by variations of the Antenna Length and width realizable by modern microfabrication techniques. The radiation efficiency of the emitting Antenna also depends on its geometry but is independent of the degree of impedance matching. The case study presented here provides the basis for experimental realizations of general optical nanocircuits based on readily available gold nanostructures and a large variety of derived novel devices.

  • impedance matching and emission properties of optical Antennas in a nanophotonic circuit
    arXiv: Optics, 2008
    Co-Authors: Jershing Huang, Thorsten Feichtner, Paolo Biagioni, Bert Hecht
    Abstract:

    An experimentally realizable prototype nanophotonic circuit consisting of a receiving and an emitting nano Antenna connected by a two-wire optical transmission line is studied using finite-difference time- and frequency-domain simulations. To optimize the coupling between nanophotonic circuit elements we apply impedance matching concepts in analogy to radio frequency technology. We show that the degree of impedance matching, and in particular the impedance of the transmitting nano Antenna, can be inferred from the experimentally accessible standing wave pattern on the transmission line. We demonstrate the possibility of matching the nano Antenna impedance to the transmission line characteristic impedance by variations of the Antenna Length and width realizable by modern microfabrication techniques. The radiation efficiency of the transmitting Antenna also depends on its geometry but is independent of the degree of impedance matching. Our systems approach to nanophotonics provides the basis for realizing general nanophotonic circuits and a large variety of derived novel devices.

  • Resonant optical Antennas
    Science, 2005
    Co-Authors: H. J. Eisler, P Muhlschlegel, O J F Martin, D W Pohl, Bert Hecht
    Abstract:

    We have fabricated nanometer-scate gold dipole Antennas designed to be resonant at optical frequencies. On resonance, strong field enhancement in the Antenna feed gap leads to white-light supercontinuum generation. The Antenna Length at resonance is considerably shorter than one-half the waveLength of the incident light. This is in contradiction to classical Antenna theory but in qualitative accordance with computer simulations that take into account the finite metallic conductivity at optical frequencies. Because optical. Antennas link propagating radiation and confined/enhanced optical fields, they should find applications in optical characterization, manipulation of nanostructures, and optical information processing.

Alberto Moreira - One of the best experts on this subject based on the ideXlab platform.

  • multichannel azimuth processing in scansar and tops mode operation
    IEEE Transactions on Geoscience and Remote Sensing, 2010
    Co-Authors: Nicolas Gebert, Gerhard Krieger, Alberto Moreira
    Abstract:

    Due to a system-inherent limitation, conventional synthetic aperture radar (SAR) is incapable of imaging a wide swath with high geometric resolution. This restriction can be overcome by systems with multiple receive channels in combination with an additional digital signal processing network. So far, the application of such digital beamforming algorithms for high-resolution wide-swath SAR imaging has been restricted to multichannel systems in stripmap operation. However, in stripmap mode, the overall azimuth Antenna Length restricts the achievable swath width, thus preventing very wide swaths as requested by future SAR missions. Consequently, new concepts for ultrawide-swath imaging are needed. A promising candidate is a SAR system with multiple azimuth channels being operated in burst mode. This paper analyzes innovative ScanSAR and Terrain Observation by Progressive Scans (TOPS) system concepts with regard to multichannel azimuth processing. For this, the theoretical analyses, performance figures, and SAR signal processing, which had previously been derived for multichannel stripmap mode, are extended to systems operating in burst modes. The investigations reveal that multichannel ScanSAR systems enable the imaging of ultrawide swaths with high azimuth resolution and compact Antenna Lengths. These considerations are embedded in a multichannel ScanSAR system design example to demonstrate its capability to image an ultrawide swath of 400 km with a high geometric resolution of 5 m. In a next step, this system is adapted to TOPS mode operation, including an innovative “staircase” multichannel processing approach optimized for TOPS.

  • sar signal reconstruction from non uniform displaced phase centre sampling in the presence of perturbations
    International Geoscience and Remote Sensing Symposium, 2005
    Co-Authors: Nicolas Gebert, Gerhard Krieger, Alberto Moreira
    Abstract:

    The displaced phase centre (DPC) technique enables a wide swath SAR with high azimuth resolution. In classic DPC systems, the pulse repetition frequency (PRF), sensor velocity and Antenna Length underlie a stringent timing requirement and any deviation will result in a non-uniform sampling of the syn­thetic aperture. This restriction can be overcome by the use of a recon­struction algorithm, which enables a recovery of the unambiguous Doppler spectrum also in case of a non-uniform sampling. This paper ex­plains limitations of the reconstruction imposed by the processing and the impacts on the ambiguity suppression. The potential of the algorithm when applied to DPC systems like TerraSAR-X with its split receive Antenna is demon­strated and the benefits re­sulting from the additional receive ap­ertur e regarding swath width and resolution are pointed out. Further on, the impact of ad­ditive and phase noise on the recon­struction and its sensitivity against these perturbations are shown.

  • sar signal reconstruction from non uniform displaced phase centre sampling
    International Geoscience and Remote Sensing Symposium, 2004
    Co-Authors: Gerhard Krieger, Nicolas Gebert, Alberto Moreira
    Abstract:

    The displaced phase centre (DPC) technique enables a wide swath SAR with high azimuth resolution. In a classic DPC system, the PRF has to be chosen such that the SAR carrier moves just one half of its Antenna Length between subsequent radar pulses. Any deviation from this PRF results in a non-uniform sampling of the synthetic aperture. This paper shows that an unambiguous reconstruction of the SAR signal is also possible in case of such a non-optimum PRF. For this, an innovative reconstruction algorithm is derived, which enables a recovery of the unambiguous Doppler spectrum also in case of a non-uniform sampling of the synthetic aperture. This algorithm also has a great potential for multistatic satellite constellations as well as the dual receive Antennas in Radarsat II and TerraSAR-X

  • unambiguous sar signal reconstruction from nonuniform displaced phase center sampling
    IEEE Geoscience and Remote Sensing Letters, 2004
    Co-Authors: Gerhard Krieger, Nicolas Gebert, Alberto Moreira
    Abstract:

    The displaced phase center (DPC) technique will enable a wide-swath synthetic aperture radar (SAR) with high azimuth resolution. In a classic DPC system, the pulse repetition frequency (PRF) has to be chosen such that the SAR carrier moves just one half of its Antenna Length between subsequent radar pulses. Any deviation from this PRF will result in a nonuniform sampling of the synthetic aperture. This letter derives an innovative reconstruction algorithm and shows that an unambiguous reconstruction of a SAR signal is possible for nonuniform sampling of the synthetic aperture. This algorithm will also have great potential for multistatic satellite constellations as well as the dual receive Antenna mode in Radarsat 2 and TerraSAR-X.

Frank R Moore - One of the best experts on this subject based on the ideXlab platform.

  • the impact of radio tags on ruby throated hummingbirds archilochus colubris
    The Condor, 2014
    Co-Authors: Theodore J Zenzal, Robert H Diehl, Frank R Moore
    Abstract:

    ABSTRACT Radiotelemetry has advanced the field of wildlife biology, especially with the miniaturization of radio-tags. However, the major limitation when radio-tagging birds is the size of the animal to which a radio-tag can be attached. We tested how miniature radio-tags affected flight performance and behavior of Ruby-throated Hummingbirds (Archilochus colubris), possibly the smallest bird species that has been fitted with radio-tags. Using eyelash adhesive, we fitted hatch-year individuals (n = 20 males, n = 15 females) with faux radio-tags of 3 sizes that varied in mass and Antenna Length (220 mg, 12.7 cm; 240 mg, 12.7 cm; and 220 mg, 6.35 cm), then filmed the birds in a field aviary to quantify activity budgets. We also estimated flight range using flight simulation models. When the 3 radio-tag packages were pooled for analysis, the presence of a radio-tag significantly decreased both flight time (∼8%) and modeled flight range (∼23%) in comparison to control birds. However, a multiple-comparison anal...

  • the impact of radio tags on ruby throated hummingbirds archilochus colubris
    bioRxiv, 2014
    Co-Authors: Theodore J Zenzal, Robert H Diehl, Frank R Moore
    Abstract:

    Radio telemetry has advanced the field of wildlife biology, especially with the miniaturization of radio-tags. However, the major limitation faced with radio-tagging birds is the size of the animal to which a radio-tag can be attached. We tested how miniature radio-tags affected flight performance and behavior of Ruby-throated Hummingbirds (Archilochus colubris), possibly the smallest bird species to be fitted with radio-tags. Using eyelash adhesive, we fitted hatch year individuals (n=20 males and 15 females) with faux radio-tags of three sizes varying in mass and Antenna Length (220mg-12.7cm, 240mg-12.7cm, and 220mg-6.35cm), then filmed the birds in a field aviary to quantify activity budgets. We also estimated flight range using flight simulation models. When the three radio-tag packages were pooled for analysis, the presence of a radio-tag significantly decreased both flight time (-8%) and modeled flight range (-23%) when compared to control birds. However, a multiple comparison analysis between the different packages revealed that there was a significant difference in flight time when the larger radio-tag package (240mg) was attached and no significant difference in flight time when the lighter radio-tag packages (220mg) were attached. Our results are similar to other studies which analyzed the flight time or flight range of birds wearing radio-tags. Therefore, currently available light weight radio-tags (≤220mg) may be a new option to aid in the study of hummingbird biology. Future study should focus upon the additional drag created by the radio-tag and the effects of the lightest radio-tag packages on free ranging birds. These studies would provide additional information to determine the feasibility on the use of radio-tags to study hummingbird biology. Keywords: radio transmitters, radio telemetry, Ruby-throated Hummingbirds, Archilochus colubris, radio-tagging, behavior, flight simulations, migration

Tom Thomas - One of the best experts on this subject based on the ideXlab platform.

  • Effects of Antenna Length and material on output power and detection of miniature radio transmitters
    Hydrobiologia, 2007
    Co-Authors: John W. Beeman, Neil Bower, Steve Juhnke, Laura Dingmon, Mike Tillaart, Tom Thomas
    Abstract:

    The optimal Antenna of transmitters used in small aquatic animals is often a compromise between efficient radio wave propagation and effects on animal behavior. Radio transmission efficiency generally increases with diameter and Length of the conductor, but increased Antenna Length or weight can adversely affect animal behavior. We evaluated the effects of changing Antenna Length and material on the subsequent tag output power, reception, and detection of tagged fish. In a laboratory, we compared the relative signal strengths in water of 150 MHz transmitters over a range of Antenna Lengths (from 6 to 30 cm) and materials (one weighing about half of the other). The peak relative signal strengths were at 20 and 22 cm, which are approximately one waveLength underwater at the test frequency. The peak relative signal strengths at these Lengths were approximately 50% greater than those of 30 cm Antennas, a Length commonly used in fisheries research. Few significant differences were present in distances for the operator to hear or the telemetry receiver to decode transmitters from a boat-mounted receiving system based on Antenna Length, but the percent of tagged fish detected passing a hydroelectric dam fitted with an array of receiving systems was significantly greater at the Antenna Length with peak output power in laboratory tests. This study indicates careful choice of Antenna Length and material of small transmitters can be used to reduce weight and possible Antenna effects on animal behavior, to maximize tag output power and detection, or to balance these factors based on the needs of the application.