The decay of radar echoes from meteors with particular reference to their use in the determination of temperature fluctuations near the mesopause

1995 ◽  
Vol 13 (10) ◽  
pp. 1104-1106 ◽  
Author(s):  
W. Jones
Keyword(s):  
Diffusion Coefficient ◽  
Kinetic Theory ◽  
Decay Time ◽  
Temperature Fluctuations ◽  
Atmospheric Temperature ◽  
Initial Distribution ◽  
Correct Result ◽  
Radar Echoes ◽  
Decay Times ◽  
Radar Echo

Abstract. The rate of decay of a radar echo from an ionised meteor train will be governed by the diffusion coefficient of the plasma and this in turn will depend on the temperature. Very recently the temperature fluctuations near the mesopause have been monitored by this means, by the recording of the decay times of underdense trains. The usual derivation of the precise expression relating the underdense echo decay time to the temperature contains two important assumptions, (i) that the train is created with a Gaussian ionisation profile, and (ii) that kinetic theory may be applied to calculate the diffusion coefficient. We investigate the effect of these assumptions, showing that the first assumption is unnecessary, an underdense backscatter echo decaying exponentially with a decay time equal to λ2/(32π2D), where λ is the wavelength and D the diffusion coefficient, independently of the initial distribution. However, the second assumption is shown to be incorrect, and whereas according to kinetic theory D∝T1/2/ρ, where T and ρ are the atmospheric temperature and density, the correct result is D∝Tρ. This leads to an appreciable correction to the results for the temperature fluctuations.

SCINTILLATION MECHANISM OF Ce3+ DOPED Gd2SiO5

2001 ◽  
Vol 15 (28n30) ◽  
pp. 3877-3880 ◽  
Author(s):  
K. MORI ◽  
M. YOKOYA ◽  
H. NISHIMURA ◽  
M. NAKAYAMA ◽  
H. ISHIBASHI
Keyword(s):  
Diffusion Coefficient ◽  
Excitation Energy ◽  
Decay Time ◽  
Gamma Ray ◽  
Diffusion Time ◽  
The Core ◽  
Decay Times ◽  
Gamma Ray Irradiation

Measuring the spectra of absorption, luminescence and excitation, and the decay times of the luminescence, at various temperatures, we investigate the scintillation mechanism of Ce 3+ doped Gd 2 SiO 5 (GSO:Ce). We conclude that the excitation energy created by gamma-ray irradiation relaxes to the core exciton states formed by the 4f-4f transitions of Gd 3+, and the core exciton migrates to collide with Ce 3+, and transfers the energy to Ce 3+ to emit the luminescence. We also conclude that the decay time of the Ce 3+ luminescence in GSO:Ce (70 ns for the case of 0.5 mol% of Ce concentration) is decided by the diffusion time of the core exciton. A very small value for the diffusion coefficient of the core exciton is estimated to be 7× 10-7 cm2/s.

Simulation of Stepped-Frequency LFM Radar Echo Based on FPGA

2012 ◽  
Vol 198-199 ◽  
pp. 948-953
Author(s):  
Jian Ping Ou ◽  
Sheng Qi Liu ◽  
Wei Niu
Keyword(s):  
Moving Target ◽  
Direct Digital Synthesis ◽  
Implementation Framework ◽  
Radar Echoes ◽  
Radar Echo ◽  
Digital Synthesis ◽  
Physical Simulations ◽  
Stepped Frequency ◽  
Logic Resource

An implementation framework of stepped-frequency LFM (SF-LFM) radar echoes simulator is presented in the paper based on the decomposition and calculation of SF-LFM radar echoes of a moving target. The proposed method can be implemented conveniently with direct digital synthesis (DDS) logic resource. The feasibility of this resolution is verified with computer and semi-physical simulations experiments.

Properties of spontaneous inhibitory synaptic currents in cultured rat spinal cord and medullary neurons

1996 ◽  
Vol 76 (1) ◽  
pp. 448-460 ◽  
Author(s):  
C. A. Lewis ◽  
D. S. Faber
Keyword(s):  
Spinal Cord ◽  
Time Constant ◽  
Decay Time ◽  
Cultured Cells ◽  
Decay Time Constant ◽  
Inhibitory Synapses ◽  
Gamma Aminobutyric Acid ◽  
Postsynaptic Receptor ◽  
Decay Times ◽  
Medullary Neurons

1. To identify the type(s) and properties of inhibitory postsynaptic receptor(s) involved in synaptic transmission in cultured rat embryonic spinal cord and medullary neurons, we have used whole cell patch-clamp techniques to record miniature inhibitory postsynaptic currents (mIPSCs) in the presence of tetrodotoxin, DL-2-amino-5-phosphonovaleric acid, and 6-cyano-7-nitroquinoxaline-2,3-dione. 2. The mIPSCs recorded from both spinal cord and medullary neurons had skewed amplitude distributions. 3. The glycinergic antagonist strychnine and the GABAergic antagonist bicuculline each decreased both the frequency and mean peak amplitudes of mIPSCs. We conclude that both glycine and gamma-aminobutyric acid (GABA) are neurotransmitters at inhibitory synapses in our cultured cells. 4. Most (approximately 96-97%) mIPSCs decay with single-exponential time constants, and decay time distributions were consistently best fitted by the sum of four Gaussians with decay constants as follows: D1 = 5.8 +/- 0.1 (SE) ms (n = 63), D2 = 12.2 +/- 0.2 ms (n = 61), D3 = 23.2 +/- 0.4 ms (n = 54), and D4 = 44.7 +/- 1.0 ms (n = 57). We conclude that the four classes of decay times represent kinetically different inhibitory postsynaptic receptor populations. 5. Strychnine and bicuculline usually had one of two different effects on the mIPSC decay time constant distributions; either selective decreases in the frequency of mIPSCs with decay times in certain classes (i.e., the D1 class was reduced by bicuculline, the D2 class by strychnine, and the D3 and D4 classes by both antagonists) or a nonselective depression in the frequency of mIPSCs with decay times in all four classes. The particular effect observed in a given neuron was correlated with the presence or absence of ATP and guanosine 5'-triphosphate (GTP) in the patch pipette. Namely, in 71% of the antagonist applications where the pipette contained ATP and GTP, the result was a nonselective decrease in mIPSCs in all decay time constant classes. Conversely, in 54% of the antagonist applications in their absence, the result was a selective decrease in the frequency of mIPSCs in specific decay time constant classes. 6. In some experiments, mIPSCs reappeared in antagonist solution after an essentially complete block. Recovery from block in the continued presence of antagonist was never observed in the absence of ATP and GTP (8 neurons), and, at the same time, 5 of 9 neurons patched with ATP and GTP in the pipette did show recovery (56%).

scholarly journals Improving The Accuracy Of Selection Of Bird Radar Echoes Against A Background Of Atomized Clouds And Atmospheric Inhomogeneities

The Ring ◽  
2015 ◽  
Vol 37 (1) ◽  
pp. 3-18
Author(s):  
Leonid Dinevich
Keyword(s):  
Bird Migration ◽  
Meteorological Conditions ◽  
Flight Safety ◽  
Selection Algorithm ◽  
Radar Echoes ◽  
Military Aviation ◽  
Radar Echo ◽  
Reflected Signal ◽  
Selection Of ◽  
Polarization Fluctuation

Abstract The algorithm for bird radar echo selection was developed in Israel and has been successfully used for many years to monitor birds in periods of massive intercontinental migration in order to ensure flight safety in civil and military aviation. However, it has been found that under certain meteorological conditions the bird echo selection algorithm does not filter out false signals formed by atomized clouds and atmospheric inhomogeneities. Although the algorithm is designed to identify and sift false signals, some useful echoes from smaller birds are erroneously sifted as well. This paper presents some additional features of radar echoes reflected from atmospheric formations that can be taken into account to prevent the loss of useful bird echoes. These additional features are based on the use of polarization, fluctuation and Doppler characteristics of a reflected signal. By taking these features into account we can reduce the number of false signals and increase the accuracy of the bird echo selection algorithm. The paper presents methods for using radar echoes to identify species and sizes of birds, together with recommendations on using the data to ensure flight safety during periods of massive intercontinental bird migration.

associations between aircraft measurements of turbulence and weather radar measurements1

1965 ◽  
Vol 46 (8) ◽  
pp. 443-447 ◽  
Author(s):  
Edwin Kessler ◽  
Jean T. Lee ◽  
Kenneth E. Wilk
Keyword(s):  
Weather Radar ◽  
Radar Data ◽  
Time Dependent ◽  
Aircraft Measurements ◽  
Radar Echoes ◽  
Radar Echo

Aircraft have been guided with the aid of radar data to measure turbulence in thunderstorm areas. Although turbulence is frequently encountered in areas containing highly reflective and sharp-edged echoes, no unique correspondence has been discovered between single-echo parameters and collocated within-storm turbulence. A theory embracing some of the time-dependent relationships between fields of wind and precipitation suggests that the correspondence between instantaneous distributions of radar echoes and turbulence is statistical rather than precise. Statistical bases for study of radar echo-turbulence relationships are outlined.

scholarly journals Arctic sea-ice variability is primarily driven by atmospheric temperature fluctuations

2019 ◽  
Vol 12 (6) ◽  
pp. 430-434 ◽  
Author(s):  
Dirk Olonscheck ◽  
Thorsten Mauritsen ◽  
Dirk Notz
Keyword(s):  
Sea Ice ◽  
Temperature Fluctuations ◽  
Atmospheric Temperature ◽  
Arctic Sea Ice ◽  
Arctic Sea

scholarly journals On the validity of the ambipolar diffusion assumption in the polar mesopause region

2008 ◽  
Vol 26 (11) ◽  
pp. 3439-3443 ◽  
Author(s):  
A. P. Ballinger ◽  
P. B. Chilson ◽  
R. D. Palmer ◽  
N. J. Mitchell
Keyword(s):  
Ambient Temperature ◽  
Decay Time ◽  
Ambipolar Diffusion ◽  
Northern Sweden ◽  
Mesopause Region ◽  
Decay Times ◽  
Meteor Trail ◽  
Temperature And Pressure ◽  
Ion Recombination ◽  
Meteor Trails

Abstract. The decay of underdense meteor trails in the polar mesopause region is thought to be predominantly due to ambipolar diffusion, a process governed by the ambient temperature and pressure. Hence, observations of meteor decay times have been used to indirectly measure the temperature of the mesopause region. Using meteor observations from a SKiYMET radar in northern Sweden during 2005, this study found that weaker meteor trails have shorter decay times (on average) than relatively stronger trails. This suggests that processes other than ambipolar diffusion can play a significant role in trail diffusion. One particular mechanism, namely electron-ion recombination, is explored. This process is dependent on the initial electron density within the meteor trail, and can lead to a disproportionate reduction in decay time, depending on the strength of the meteor.

Persistent Photoconductivity in p-Type 4H-SiC Bulk Crystals

2013 ◽  
Vol 740-742 ◽  
pp. 413-416 ◽  
Author(s):  
Takafumi Okuda ◽  
Hiroki Miyake ◽  
Tsunenobu Kimoto ◽  
Jun Suda
Keyword(s):  
Decay Time ◽  
Room Temperature ◽  
Chemical Vapor ◽  
Persistent Photoconductivity ◽  
Bulk Crystals ◽  
Decay Times ◽  
Photoconductivity Decay ◽  
Increasing Temperature ◽  
P Type ◽  
Homoepitaxial Layers

We investigated the photoconductivity decay characteristics of p-type 4H-SiC bulk crystals grown by a modified Lely method by differential microwave photoconductance decay (μ-PCD) measurements using a 349-nm laser as an excitation source. We observed persistent photoconductivity (PPC) in the p-type SiC bulk crystals. The decay time at room temperature was 2600 μs. The decay time decreased with increasing temperature, resulting in 120 μs at 250oC, and the activation energy of the decay times was determined to be 140±10 meV. Long decay characteristics were also observed by below-band-gap excitation at 523 or 1047 nm. On the other hand, no PPC was observed in p-type homoepitaxial layers grown by hot-wall chemical vapor deposition.

Sign in / Sign up

Export Citation Format

Share Document