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Aiming at the high precision Doppler application for deep space exploration, a new algorithm for Doppler modeling using the velocity and acceleration of the central object and the spacecraft is proposed. The algorithm avoids the truncation error induced by the direct use of ranging and the positional uncertainty of ephemerides interpolation. Continuous Doppler computation for a Martian orbiter lasting one week is performed, and the general computation algorithm using ranging difference is used to test the correctness of the new algorithm. In addition, one-hour length of the Doppler data is fitted with a polynomial of order 10, and the residual error is less than 0.002 mm/s. The analysis results show that the new algorithm is correct and is approximately one order of magnitude improvement in accuracy compared with the conventional modeling algorithm. [ABSTRACT FROM AUTHOR]

Background: Ocular changes have been noted during long-duration spaceflight; we studied central retinal artery (CRA) blood flow using Doppler before, during, and after long-term microgravity exposure in astronauts compared with data from a control group of nonastronauts subjected to head-down tilt (HDT). Methods: Available Doppler spectra of International Space Station (ISS) crewmembers were obtained from the NASA Lifetime Surveillance of Astronaut Health database, along with 2D ultrasound-derived measurements of the optic nerve sheath diameter (ONSD). CRA Doppler spectra and optic nerve sheath images were also obtained from healthy test subjects in an acute HDT experi-ment at 20 min of exposure (the ground-based analogue). Results: HDT CRA peak systolic velocity in the ground-based analogue group increased by an average of 3 cm 5-1 (33%) relative to seated values. ONSD at 30° of HDT increased by 0.5 mm relative to supine values. CRA Doppler spectra obtained on orbit were of excellent quality and demonstrated in-flight changes of +5 cm 5-1 (50%) compared to preflight. ONSD increased in ISS crewmembers during flight relative to before flight, with some reversal postflight. Discussion: A significant ONSD response to acute postural change and to spaceflight was demonstrated in this pre-liminary study. Increases in Doppler peak flow velocities correlated with increases in ONSD. Further investigations are warranted to corroborate the relationship between ONSD, intracranial pressure, and central reti-nal blood flow for occupational surveillance and research purposes. [ABSTRACT FROM AUTHOR]

Abstract: MIMO radar employs multiple antennas to simultaneously transmit diverse waveforms, as well as multiple antennas to receive the radar returns. This paper studies the role of waveform diversity in MIMO radar as separate and distinct from the role of the multiple transmit antennas. This is done by comparing a MIMO radar system to a scanning phased array radar which uses the same transmit and receive arrays but only a single waveform. The performance characteristics of the two systems, in terms of the ambiguity function and the spatial response, are compared for single pulse operation as well as multi-pulse operation with coherent integration. Both element-space and beam-space systems are considered. [Copyright &y& Elsevier]

Copyright of Acta Endoscopica is the property of Lavoisier and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: We derive the correct formulation of the Doppler problem in which the received signal is scaled in time by a scale factor dependent on the relative radial velocity of the transmitter and the receiver, normalized by the propagation speed in the transmission medium. For sine waves, the conventional Doppler model in which the received signal is translated in frequency is equivalent to the scale model. However, for signals with non zero bandwidth, the difference can be quite significant, as we demonstrate. We further demonstrate simple methods, based on the discrete Fourier transform (DFT) and phase differentiation of the scale CAF, by which delay and scale may be accurately estimated. [Copyright &y& Elsevier]

Introduction: Dehydration may increase the risk for decompression sickness (DCS). Since DCS most probably is caused by endogenous gas phase formation, we hypothesized that decompression will induce more venous gas emboli (VGE) in dehydrated rats compared to controls. Methods: Two groups of rats were pressurized to 0.5 MPa (5 ATA) on heliox for 16 h, and thereafter decompressed to atmospheric pressure at a rate of 0.3 MPa · min-1. The nine control rats had free access to water ad libitum whereas the eight dehydrated rats were water-deprived for 48 h before decompression. During and after decompression, VGE was measured in the vena cava for 60 mm with the Doppler technique and graded into six bubble grade (BG) categories. Body mass (BM), and food and water intake were registered daily, and venous blood samples were taken before and after pressure exposure. Results: Serum osmolality and hematocrit increased significantly in dehydrated rats (306 ± 5.2 to 315 ± 7.3 mosmol · kg-1 and 39.3 ± 4.9 to 49.6 ± 5.2%) but not in controls (300 ± 8.9 to 303 ± 6.7 mosmol · kg-1 and 40.3 ± 5.2 to 41.4 ± 6.1%) Plasma volume decreased by 9.2% (P < 0.05) and 2.8% (n.s.) in dehydrated and control rats. VGE were detected in all control animals (average BG: 2.8 ± 1.9), but only in four water-deprived rats (BG: 1.6 ± 2.2). This difference was not significant. Conclusions: Our experiments do not support the idea that dehydration increases circulatory VGE. [ABSTRACT FROM AUTHOR]

Copyright of Neurologia (Grupo ARS XXI de Comunicacion, S.A.) is the property of Grupo ARS XXI de Comunicacion, S.A. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This note provides an error bound on an estimate resulting from a simple fusion scheme combining individual estimates based on measurements of different sensing mechanisms. An important benefit of the bound is that it requires only knowledge of the individual sensor covariances rather than the complete inter-sensor covariance structure. An example drawn from a previous paper is presented to assess the benefit to the accuracy of emitter location using a Doppler sensor for which the error bound is applied to the estimate of a set of local states entering the Doppler sensor model as parameters. [ABSTRACT FROM AUTHOR]

So-called CF–FM bats are highly mobile creatures who emit long calls in which much of the energy is concentrated in a single frequency. These bats face sensor interpretation problems very similar to those of mobile robots provided with ultrasonic sensors, while navigating in cluttered environments. This paper presents biologically-inspired engineering on the use of narrowband Sonar in mobile robotics. It replicates, using robotics as a modelling medium, methods CF–FM bats use to exploit Doppler-shifts––a rich source of information not used by commercial robotic ultrasonic range sensors––in different tasks. The experimental platform for the work is RoBat, a 6 DOF biomimetic sonarhead mounted on a commercial 3 DOF mobile platform. The platform is provided with signal processing capabilities inspired by the bat's auditory system. The CF–FM bat modifies––increasing or decreasing––the carrier frequency of its own calls, compensating the Doppler-shift produced when the bat, the reflector or both are moving. This echolocating behaviour, called Doppler-shift compensation, is successfully implemented in RoBat. Inspired by this behaviour, a convoy navigation controller following a set of simple Doppler-dependent rules is successfully devised. The performance of the controller is satisfactory despite low Doppler-shift resolution caused by the lower velocity of the robot when compared to real bats. Finally, Mu¨ller's hypothesis on the use of acoustic flow by CF–FM bats for obstacle avoidance is also implemented in RoBat, resulting in a crude estimation of the target's passing distance at small bearing angles, which improves as the angle increases, nevertheless sufficing for avoiding the two reflectors of the experiment. [Copyright &y& Elsevier]

In this paper, the performance of a generalized multi-carrier Frequency Division Multiplexing (FDM) system - including Orthogonal Frequency Division Multiplexing (OFDM) and Filter-Bank Multi-Carrier (FBMC) - is analyzed in terms of normalized interference power in a fast-varying flat-fading downlink channel. The analysis is done assuming a conventional correlator-based receiver using three families of pulse shapes: orthogonal time-limited pulse shapes, orthogonal frequency-limited pulse shapes, and non-orthogonal pulse shapes. The analysis is done for the Rayleigh random channel with different Doppler spreads, and interference distribution over sub-carriers and symbols is analyzed per pulse shape. Interference reduction by reducing the bandwidth efficiency through turning off some sub-carriers and reducing symbol density is then analyzed. After that, the special ability of non-orthogonal pulse shapes to have more flexible density reduction is indexed and studied. The theoretical study, validated by Monte Carlo simulations, showed that for low, high, and extreme Doppler spreads, the appropriate pulse shapes (resp. system density) to be used are respectively time or frequency limited orthogonal pulse shapes (resp. 100%), short-tail frequency-limited pulse shapes (resp. 50%), and time and frequency limited non-orthogonal pulse shapes (resp. 25%). [ABSTRACT FROM AUTHOR]

The Doppler effect is a very useful phenomenon in both radar and sonar systems for measuring the speed of objects. Chirps have traditionally been used in these systems due to the good properties of their compressed pulse. However, these signals when emitted and/or received in motion can suffer from Range-Doppler Coupling (RDC) influencing the Time of Flight (ToF) estimation. This influence is more accentuated in the acoustic systems especially in those developed in the air environment, such as sonar or acoustic positioning systems. This work proposes the use of a Doppler effect compensation algorithm that allows ultrasonic positioning of moving objects indoors. For this, a signal has been designed consisting of a chirp and a carrier pulse that allows to take advantage of the good qualities of the chirp, at the same time that the carrier pulse measures the speed between the emitter and receiver and from it correct the RDC suffered by the chirp. By obtaining the ToF corrected for each of the emitting beacons it is possible to position the receiver in motion. Simulations and experiments have been conducted to corroborate the good performance of the proposed algorithm, obtaining the receiver position with centimeter accuracy up to 2 m/s. [ABSTRACT FROM AUTHOR]