scholarly journals High resolution general purpose D-layer experiment for EISCAT incoherent scatter radars using selected set of random codes

2002 ◽  
Vol 20 (9) ◽  
pp. 1469-1477 ◽  
Author(s):  
T. Turunen ◽  
A. Westman ◽  
I. Häggström ◽  
G. Wannberg
Keyword(s):  
Autocorrelation Function ◽  
Spatial Resolution ◽  
Measurement Problem ◽  
Short Pulse ◽  
Plasma Temperature ◽  
General Purpose ◽  
Reliable Estimate ◽  
Radio Science ◽  
Coherent Integration ◽  
Random Codes

Abstract. The ionospheric D-layer is a narrow bandwidth radar target often with a very small scattering cross section. The target autocorrelation function can be obtained by transmitting a series of relatively short coded pulses and computing the correlation between data obtained from different pulses. The spatial resolution should be as high as possible and the spatial side lobes of the codes used should be as small as possible. However, due to the short pulse repetition period (in the order of milliseconds) at any instant, the radar receives detectable scattered signals not only from the pulse illuminating the D-region but also from 3–5 ambiguous-range pulses, which makes it difficult to produce a reliable estimate near zero lag of the autocorrelation function. A new experimental solution to this measurement problem, using a selected set of 40-bit random codes with 4 µs elements giving 600 m spatial resolution is presented. The zero lag is approximated by dividing the pulse into two 20-bit codes and computing the correlation between those two pulses. The lowest altitudes of the E-layer are measured by dividing the pulse into 5 pieces of 8 bits, which allows for computation of 4 lags. In addition, coherent integration of data from four pulses is used for obtaining separately the autocorrelation function estimate for the lowest altitudes and in cases when the target contains structures with a long coherence time. Design details and responses of the experiment are given, and analysed test data are shown.Key words. Radio science (signal processing); Ionosphere (plasma temperature and density; instruments and techniques)

scholarly journals Time resolution of cosmic noise observations with acorrelation experiment

2004 ◽  
Vol 22 (5) ◽  
pp. 1687-1689 ◽  
Author(s):  
E. Nielsen ◽  
F. Honary ◽  
M. Grill
Keyword(s):  
Radio Wave ◽  
Autocorrelation Function ◽  
Spatial Resolution ◽  
Time Resolution ◽  
Noise Intensity ◽  
Signal Amplitude ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Instruments And Techniques ◽  
Cosmic Noise

Abstract. A radio wave correlation experiment using a Mills Cross technique can be used to observe the cosmic noise intensity from the ground for the purpose of determining the absorption in the ionosphere. To ensure a time resolution of 10 to 20s of the absorption observations, it is necessary that the autocorrelation function of the signal received within a wanted spatial resolution and in a given receiver is >8% of the total signal amplitude incident on that receiver.Key words. Radio Science (Instruments and techniques; Interferometry; Ionospheric physics)

scholarly journals Low frequency waves in plasmas with spatially varying electron temperature

2000 ◽  
Vol 18 (12) ◽  
pp. 1613-1622 ◽  
Author(s):  
P. Guio ◽  
S. Børve ◽  
H. L. Pécseli ◽  
J. Trulsen
Keyword(s):  
Numerical Simulation ◽  
Electron Temperature ◽  
Acoustic Waves ◽  
Low Frequency ◽  
Plasma Temperature ◽  
Electrostatic Waves ◽  
Radio Science ◽  
Particle In Cell ◽  
Ionosphere Plasma ◽  
Low Frequency Waves

Abstract. Low frequency electrostatic waves are studied in magnetized plasmas with an electron temperature which varies with position in a direction perpendicular to the magnetic field. For wave frequencies below the ion cyclotron frequency, the waves need not follow any definite dispersion relation. Instead a band of phase velocities is allowed, with a range of variation depending on the maximum and minimum values of the electron temperature. Simple model equations are obtained for the general case which can be solved to give the spatial variation of a harmonically time varying potential. A simple analytical model for the phenomenon is presented and the results are supported by numerical simulations carried out in a 2½-dimensional particle-in-cell numerical simulation. We find that when the electron temperature is striated along B0 and low frequency waves (ω ≪ Ωci) are excited in this environment, then the intensity of these low frequency waves will be striated in a manner following the electron temperature striations. High frequency ion acoustic waves (ω ≫ Ωci) will on the other hand have a spatially more uniform intensity distribution.Key words: Ionosphere (plasma temperature and density) · Radio science (waves in plasma) · Space plasma physics (numerical simulation studies)

scholarly journals Moving target coherent integration method for non‐coherent short pulse radar

2019 ◽  
Vol 13 (6) ◽  
pp. 953-960 ◽  
Author(s):  
Haibo Wang ◽  
Wenhua Huang ◽  
Yue Jiang ◽  
Tao Ba
Keyword(s):  
Integration Method ◽  
Short Pulse ◽  
Moving Target ◽  
Pulse Radar ◽  
Coherent Integration

An Experimental and Computational Study of Temperature and Strain Fields in Metal Cutting

2001 ◽  
Author(s):  
Alan T. Zehnder ◽  
Yogesh K. Potdar ◽  
Xiaomin Deng ◽  
Chandrakant Shet
Keyword(s):  
Spatial Resolution ◽  
Metal Cutting ◽  
Computational Study ◽  
Orthogonal Cutting ◽  
Critical Role ◽  
Rake Angle ◽  
General Purpose ◽  
Temperature Fields ◽  
Ir Detectors ◽  
Strain Fields

Abstract Metal cutting is a thermo-mechanically coupled process in which plasticity induced heating and friction play a critical role. In this paper, we outline a methodology that combines high resolution experiments with numerical simulations. The simulations were performed with a general purpose finite element code. With this code we evaluate the effects of chip-tool interface friction and rake angle on temperature and cutting force and show that results for residual stresses in the workpiece are consistent with experimental data. We hypothesize that by closely coupling simulations to fine scale spatial and temporal experimental measurements of temperature and strain fields, questions related to choice of parameters in FE simulations can be resolved. We have designed and conducted orthogonal cutting experiments to measure temperatures, using IR detectors, with a spatial resolution of 27 × 27 μm and time scale of 200 ns. Experimentally obtained temperature fields are compared with FE results. We also obtain deformation fields with a spatial resolution of 50 × 50 μm.

scholarly journals Software Radar signal processing

2005 ◽  
Vol 23 (1) ◽  
pp. 109-121 ◽  
Author(s):  
T. Grydeland ◽  
F. D. Lind ◽  
P. J. Erickson ◽  
J. M. Holt
Keyword(s):  
Signal Processing ◽  
Cross Correlation ◽  
General Purpose ◽  
Radar Signal ◽  
Software Infrastructure ◽  
Computing Systems ◽  
Radio Science ◽  
Software Patterns ◽  
Incoherent Scatter ◽  
Radar Systems

Abstract. Software infrastructure is a growing part of modern radio science systems. As part of developing a generic infrastructure for implementing Software Radar systems, we have developed a set of reusable signal processing components. These components are generic software-based implementations for use on general purpose computing systems. The components allow for the implementation of signal processing chains for radio frequency signal reception, correlation-based data processing, and cross-correlation-based interferometry. The components have been used to implement the signal processing necessary for incoherent scatter radar signal reception and processing as part of the latest version of the Millstone Hill Data Acquisition System (MIDAS-W). Several hardware realizations with varying capabilities have been created, and these have been used successfully with different radars. We discuss the signal processing components in detail, describe the software patterns in which they are used, and show example data from the Millstone Hill, EISCAT Svalbard, and SOUSY Svalbard radars.

scholarly journals Performance Evaluation of Fifth-Generation Ultra-High-Resolution SPECT System with Two Stationary Detectors and Multi-Pinhole Imaging

2020 ◽  
Author(s):  
Jan V Hoffmann ◽  
Jan P Janssen ◽  
Takayuki Kanno ◽  
Takayuki Shibutani ◽  
Masahisa Onoguchi ◽  
...  
Keyword(s):  
High Resolution ◽  
Spatial Resolution ◽  
Single Photon ◽  
Photon Emission ◽  
Small Animal ◽  
High Sensitivity ◽  
General Purpose ◽  
Emission Computed Tomography ◽  
High Count ◽  
Spect System

Abstract Background: Small-animal single-photon emission computed tomography (SPECT) systems with multi-pinhole collimation and large stationary detectors have advantages compared to systems with moving small detectors. These systems benefit from less labour-intensive maintenance and quality control as fewer prone parts are moving, higher accuracy for focused scans and maintaining high resolution with increased sensitivity due to focused pinholes on the field of view. This study aims to investigate the performance of a novel ultra-high-resolution scanner with two-detector-configuration (U-SPECT5-E) and to compare its image quality to a conventional micro-SPECT system with three stationary detectors (U-SPECT+).Methods: The new U-SPECT5-E with two stationary detectors was used for acquiring data with 99mTc-filled point source, hot-rod and uniformity phantoms to analyse sensitivity, spatial resolution, uniformity and contrast-to-noise ratio (CNR). Three dedicated multi-pinhole mouse collimators with 75 pinholes each and 0.25-, 0.60- and 1.00-mm pinholes for extra ultra-high resolution (XUHR-M), general-purpose (GP-M) and ultra-high sensitivity (UHS-M) imaging were examined. For CNR analysis, four different activity ranges representing low- and high-count settings were investigated for all three collimators. The experiments for the performance assessment were repeated with the same GP-M collimator in the three-detector U-SPECT+ for comparison. Results: Peak sensitivity was 237 cps/MBq (XUHR-M), 847 cps/MBq (GP-M), 2054 cps/MBq (UHS-M) for U-SPECT5-E and 1710 cps/MBq (GP-M) for U-SPECT+. In the visually analysed sections of the reconstructed mini Derenzo phantom, rods as small as 0.35 mm (XUHR-M), 0.50 mm (GP-M) for the two-detector as well as the three-detector SPECT and 0.75 mm (UHS-M) were resolved. Uniformity for maximum resolution recorded 40.7% (XUHR-M), 29.1% (GP-M, U-SPECT5-E), 16.3% (GP-M, U-SPECT+) and 23.0% (UHS-M), respectively. UHS-M reached highest CNR values for low-count images; for rods smaller than 0.45 mm, acceptable CNR was only achieved by XUHR-M. GP-M was superior for imaging rods sized from 0.60-1.50 mm for intermediate activity concentrations. U-SPECT5-E and U-SPECT+ both provided comparable CNR.Conclusions: While uniformity and sensitivity are negatively affected by the absence of a third detector, the investigated U-SPECT5-E system with two stationary detectors delivers excellent spatial resolution and CNR comparable to the performance of an established three-detector-setup.

scholarly journals Investigation of dominant states for dielectronic recombination in short-pulse laser-produced aluminum plasma

2012 ◽  
Vol 31 (1) ◽  
pp. 1-8 ◽  
Author(s):  
V. Stancalie
Keyword(s):  
Pulse Laser ◽  
Short Pulse ◽  
Energy Levels ◽  
Resonance Energy ◽  
Dielectronic Recombination ◽  
General Purpose ◽  
Detailed Calculation ◽  
Close Coupling ◽  
Short Pulse Laser ◽  
Aluminum Plasma

AbstractThis paper presents the results of relativistic calculation intended specifically to investigate the dominant states for dielectronic recombination of Li-like into Be-like Al ions in short-pulse laser produced plasmas. The relativistic Dirac R-matrix calculation is performed to output resonance energy levels and rates. The target energies and orbitals are calculated with the extended average level multi-configurational Dirac-Fock method in the general-purpose relativistic atomic structure package. This type of calculation gives a set of 13 bound orbitals that is optimized over all the levels included. The resulting 13 relativistic orbitals produced 74 Jπ levels, all of which are to be used in the close-coupling expansion. To the best of our knowledge, the work reported herein describes for the first time such detailed calculation for this atomic system and the results are relevant to the short-pulse laser produced plasma modeling.

Energy Dependence of Emission Intensity and Temperature in a LIBS Plasma Using Femtosecond Excitation

2001 ◽  
Vol 55 (3) ◽  
pp. 286-291 ◽  
Author(s):  
Kristine L. Eland ◽  
Dimitra N. Stratis ◽  
David M. Gold ◽  
Scott R. Goode ◽  
S. Michael Angel
Keyword(s):  
Emission Intensity ◽  
Laser Energy ◽  
Short Pulse ◽  
Line Emission ◽  
Plasma Temperature ◽  
Background Intensity ◽  
Pulse Excitation ◽  
Intensity Increase ◽  
Breakdown Spectroscopy ◽  
Laser Induced Breakdown

In this paper, we investigate the effect of laser energy on laser-induced breakdown emission intensity and average temperature in a short-pulse plasma generated by using 140 fs laser excitation. Both line emission and continuum background intensity and plasma temperature decrease very rapidly after excitation compared to the more conventional nanosecond pulse excitation. Both emission intensity and plasma temperature increase with increasing laser energy. However, the intensity increase appears to be mostly related to the amount of material ablated. Also, nongated laser-induced breakdown spectroscopy (LIBS) is demonstrated using a high-pulse (1 kHz) pulse repetition rate.

A simulated global GM estimate of the asteroid 469219 Kamo‘oalewa for China’s future asteroid mission

2020 ◽  
Vol 493 (3) ◽  
pp. 4012-4021 ◽  
Author(s):  
W T Jin ◽  
F Li ◽  
J G Yan ◽  
T P Andert ◽  
M Ye ◽  
...  
Keyword(s):  
Software Package ◽  
Initial Conditions ◽  
Weighted Least Squares ◽  
Reliable Estimate ◽  
Distance Measurements ◽  
Radio Science ◽  
Least Squares Fit ◽  
Asteroid Mission ◽  
Sample Return Mission ◽  
Simulation Results

ABSTRACT China will launch in the forthcoming years a sample return mission called ZhengHe, to asteroid 469219 Kamo‘oalewa (provisional designation 2016HO3) and comet 133P/Elst-Pizarro. The mission will consist of an orbiter and a nano-lander. One of ZhengHe’s investigations is the radio science experiment, whose main objective is the asteroid GM estimate. In this paper, we conduct full numerical simulations of the radio science experiment using the wudogs software package, developed by Wuhan University. In addition to two-way Doppler measurements, we also include one-way on-board distance measurements. A list of parameters including the spacecraft initial conditions and the global asteroid GM are solved using a weighted least-squares fit. The simulation results indicate that the GM solution is very sensitive to the ephemeris error. We need an accuracy within 2 km on the ephemeris of the asteroid to achieve a reliable estimate of GM.

scholarly journals Performance evaluation of fifth-generation ultra-high-resolution SPECT system with two stationary detectors and multi-pinhole imaging

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Jan V. Hoffmann ◽  
Jan P. Janssen ◽  
Takayuki Kanno ◽  
Takayuki Shibutani ◽  
Masahisa Onoguchi ◽  
...  
Keyword(s):  
High Resolution ◽  
Spatial Resolution ◽  
Single Photon ◽  
Photon Emission ◽  
Small Animal ◽  
High Sensitivity ◽  
General Purpose ◽  
Emission Computed Tomography ◽  
High Count ◽  
Spect System

Abstract Background Small-animal single-photon emission computed tomography (SPECT) systems with multi-pinhole collimation and large stationary detectors have advantages compared to systems with moving small detectors. These systems benefit from less labour-intensive maintenance and quality control as fewer prone parts are moving, higher accuracy for focused scans and maintaining high resolution with increased sensitivity due to focused pinholes on the field of view. This study aims to investigate the performance of a novel ultra-high-resolution scanner with two-detector configuration (U-SPECT5-E) and to compare its image quality to a conventional micro-SPECT system with three stationary detectors (U-SPECT+). Methods The new U-SPECT5-E with two stationary detectors was used for acquiring data with 99mTc-filled point source, hot-rod and uniformity phantoms to analyse sensitivity, spatial resolution, uniformity and contrast-to-noise ratio (CNR). Three dedicated multi-pinhole mouse collimators with 75 pinholes each and 0.25-, 0.60- and 1.00-mm pinholes for extra ultra-high resolution (XUHR-M), general-purpose (GP-M) and ultra-high sensitivity (UHS-M) imaging were examined. For CNR analysis, four different activity ranges representing low- and high-count settings were investigated for all three collimators. The experiments for the performance assessment were repeated with the same GP-M collimator in the three-detector U-SPECT+ for comparison. Results Peak sensitivity was 237 cps/MBq (XUHR-M), 847 cps/MBq (GP-M), 2054 cps/MBq (UHS-M) for U-SPECT5-E and 1710 cps/MBq (GP-M) for U-SPECT+. In the visually analysed sections of the reconstructed mini Derenzo phantoms, rods as small as 0.35 mm (XUHR-M), 0.50 mm (GP-M) for the two-detector as well as the three-detector SPECT and 0.75 mm (UHS-M) were resolved. Uniformity for maximum resolution recorded 40.7% (XUHR-M), 29.1% (GP-M, U-SPECT5-E), 16.3% (GP-M, U-SPECT+) and 23.0% (UHS-M), respectively. UHS-M reached highest CNR values for low-count images; for rods smaller than 0.45 mm, acceptable CNR was only achieved by XUHR-M. GP-M was superior for imaging rods sized from 0.60 to 1.50 mm for intermediate activity concentrations. U-SPECT5-E and U-SPECT+ both provided comparable CNR. Conclusions While uniformity and sensitivity are negatively affected by the absence of a third detector, the investigated U-SPECT5-E system with two stationary detectors delivers excellent spatial resolution and CNR comparable to the performance of an established three-detector-setup.

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