LONG DURATION ECHOES FROM AURORA, METEORS, AND IONOSPHERIC BACK-SCATTER

1953 ◽  
Vol 31 (2) ◽  
pp. 171-181 ◽  
Author(s):  
D. W. R. McKinley ◽  
Peter M. Millman
Keyword(s):  
Long Range ◽  
High Frequency ◽  
The Other ◽  
Very High Frequency ◽  
Long Duration ◽  
E Region ◽  
Very High ◽  
Visual Observations

In the course of the Ottawa meteor program some unusual echoes have been detected on 33 Mc. Echoes from the aurora are discussed and correlated with visual observations. Two mechanisms of radio reflections from the aurora have been proposed but the data here presented are insufficient to favor one over the other. On Aug. 4, 1948, six extremely long duration meteor echoes were observed which may have been due to abnormal ionospheric conditions. From time to time since August, 1948, a weak semipermanent echo has been recorded, usually appearing at a range of about 80 km., and enduring up to an hour. It is suggested that this echo is due to back-scatter from the same sources in the lower E-region that are presumed to be responsible for long-range very high frequency propagation.

scholarly journals Skipping of the very-high-frequency structural particle de (的) in Chinese reading

2018 ◽  
Vol 71 (1) ◽  
pp. 152-160 ◽  
Author(s):  
Chuanli Zang ◽  
Manman Zhang ◽  
Xuejun Bai ◽  
Guoli Yan ◽  
Bernhard Angele ◽  
...  
Keyword(s):  
Experimental Psychology ◽  
High Frequency ◽  
The Other ◽  
Chinese Reading ◽  
Very High Frequency ◽  
Sentential Context ◽  
Parafoveal Preview ◽  
Single Character ◽  
Boundary Paradigm ◽  
Very High

How do readers decide whether to skip or fixate a word? Angele and Rayner [2013. Processing the in the parafovea: Are articles skipped automatically? Journal of Experimental Psychology: Learning, Memory, and Cognition, 39, 649–662] showed that English readers base skipping decisions on the parafoveal information available, but not the sentential context. Due to the increased visual density of the language, Chinese readers may be able to process a parafoveal word and integrate it with the sentence context to a greater extent than English readers. Consequently, influences on skipping decisions in Chinese may differ from those in English. In a boundary paradigm experiment, participants read sentences containing a single-character target verb (e.g., 取 meaning get) whose preview was manipulated in three conditions: identity preview; a preview consisting of the syntactically anomalous high-frequency structural particle de (的), or a pseudocharacter preview. The results showed that Chinese readers were more likely to skip the target when the preview was de than in either of the other conditions, suggesting that de-skipping is triggered by the parafoveal preview of a highly frequent particle word rather than on the likelihood of the upcoming word given the sentential context.

DEPENDENCE OF INTEGRATED DURATION OF METEOR ECHOES ON WAVELENGTH AND SENSITIVITY

1954 ◽  
Vol 32 (7) ◽  
pp. 450-467 ◽  
Author(s):  
D. W. R. McKinley
Keyword(s):  
Short Duration ◽  
High Frequency ◽  
Time Of Day ◽  
Very High Frequency ◽  
Forward Scatter ◽  
Long Duration ◽  
Meteor Trails ◽  
Cedar Rapids ◽  
Very High

The reflecting properties of short-duration and long-duration echoes from meteor trails are examined. For short-duration echoes only, the observed relation between relative numbers and durations of meteor echoes is independent of wavelength, the time of day, or the presence of a strong shower. Integrated duration times are determined from back-scatter experiments on 9.22 m., 5.35 m., and 2.83 m., and are found to vary with the 3.5th power of the wavelength, for either short- or long-duration echoes. The integrated echo power depends on the 6th power of the wavelength. The effect of changing the equipment sensitivity is considered. The data from the back-scatter observations are used to predict the integrated duration times in the forward-scatter case, and in particular, it is shown that the results of the Cedar Rapids – Sterling very-high-frequency experiment may be explained by meteoric reflections.

scholarly journals The hyperfine structure of the lines of the arc spectrum of rubidium

1933 ◽  
Vol 139 (839) ◽  
pp. 673-682 ◽  
Keyword(s):  
Fine Structure ◽  
High Frequency ◽  
The Other ◽  
Resolving Power ◽  
Nuclear Moment ◽  
Very High Frequency ◽  
Centre Of Gravity ◽  
Helium Neon ◽  
Very High ◽  
Echelon Grating

The structure of the lines of the arc spectrum of rubidium was investigated with a reflexion echelon grating of high resolving power, the light source being a tube containing helium neon mixture at about ½ mm. pressure and a small quantity of rubidium; this tube was fitted with external electrodes and excited with an oscillator of very high frequency. The two resonance lines—7947 and 7800—were found to possess the same fine structure, and each possessed four components: at 0·00, —0·09, —0·19 and —0·23 cm. -1 ; the two outer components, 0·00 and —0·23 cm. -1 , are weak and the two inner components are strong. The lines 4215 and 4201 were found to possess three components; at 0·00, —0·09 and —0·20 cm. -1 . The line at the latter point was slightly broadened. This was presumed to correspond to the same structure as that observed in the resonance lines, the broadened line corresponding to —0·19 and —0·23 unresolved. This observed structure is explained as arising from the 5S 1/2 level; the two outer, weak, components arising from the isotope 87 and corresponding to a separation into two levels, 0·23 cm. -1 apart, in the 5S 1/2 level; while the two inner, stronger, components arise from the other isotope, 85, and correspond to a similar separation of 0·10 cm. -1 . The centre of gravity of the levels of Rb 85 is displaced about 0·02 cm. -1 from that of the levels of Rb 87. Measurements on the intensities of the components of 4201 show that the probable value for the nuclear moment of Rb 85 is 3/2, but the accuracy is not sufficiently high to enable the value for the scarcer isotope Rb 87 to be determined with certainty; the probable value is, however, 5/2. The magnetic moment of the nucleus of Rb 87 is shown to be approximately two and a half times as great as that of Rb 85.

The evolution of complex Es observed by multi instruments over low-latitude China

2021 ◽  
Author(s):  
Wenjie Sun ◽  
Baiqi Ning ◽  
Lianhuan Hu ◽  
Xiukuan Zhao ◽  
Guozhu Li
Keyword(s):  
High Frequency ◽  
Electron Content ◽  
Very High Frequency ◽  
Low Latitude ◽  
Radar Backscatter ◽  
Vhf Radar ◽  
Total Electron ◽  
E Region ◽  
Sporadic E ◽  
Very High

<p>Early and recent observations suggested that E-region field aligned irregularities (FAIs) related closely to the sporadic E (Es) layer of the ionosphere. The Sanya (18.3 ºN, 109.6 ºE) very high frequency (VHF) radar can operate at ionospheric irregularities mode for the detection of 3-m scale FAIs. The development of a portable digital ionosonde (PDI) which is collocated with the Sanya VHF radar can operate with temporal periods down to 1 minute, facilitating the capability of capturing the fast evolution of Es structures. But the low spatial resolution of the two kinds of instruments makes it difficult to depict the horizontal morphology of the Es structures and E-region FAIs. Since the capability of ground-based GNSS in strong Es detection was presented, it serves as a perfect supplement for the investigation of E region of the ionosphere. So comprehensive observation with multi kinds of instruments makes it possible to reveal the relationship and mechanisms of Es and E-region FAIs.</p><p>A complex daytime sporadic E (Es) case with extremely high critical frequency (foEs) was observed over the low latitude of China on 19 May 2018. Simultaneous observational results from two very high frequency (VHF) radars, two ionosondes, and multiple Global Navigation Satellite System total electron content and scintillation receivers are analyzed to investigate the evolution of the complex Es occurrence, which consisted of a relatively weak ambient Es layer (foEs < 8 MHz) and band-like strong Es structures (foEs > 17 MHz) drifting from higher latitude. The strong Es structures elongated more than 500 km in the northwest-southeast direction, drifted southwestward at a speed of ~65 m/s. VHF radar backscatter echoes were generated when the strong Es structures passed the radar field of view, with different echo patterns due to different radar and antenna configurations. No VHF radar backscatter echo was associated with the ambient Es layer.</p>

Reproduction in the Herpetofaunal Community of a Banksia Woodland Near Perth, W.a.

1980 ◽  
Vol 28 (3) ◽  
pp. 435 ◽  
Author(s):  
C Davidge
Keyword(s):  
Surface Water ◽  
High Frequency ◽  
Early Summer ◽  
The Other ◽  
Reproductive Pattern ◽  
Very High Frequency ◽  
The Third ◽  
Frog Species ◽  
Second Year ◽  
Very High

Twelve species of lizards (Agamidae, Scincidae, Pygopodidae) and three species of frogs (Leptodac- tylidae) comprise the herpetofaunal community of a Banksia woodland under a mediterranean-type climate in Western Australia. The reptiles bred in September-November and laid eggs in early summer. The requirement of surface water for tadpole development for two of the frog species restricted their breeding time to winter and necessitated their migration from the study area, where no water was avail- able. The third species of frog, Myobatrachus gouldii, lacks an aquatic stage. Its reproductive pattern coincided with neither that of the reptiles nor the other frogs. Collections of most species in the com- munity were not equally divided between sexes. For reptiles, this possibly was owing to differential trapping of the sexes. The very high frequency of capture of female frogs, other than those of M. gouldii, was probably related to differential dispersal of the sexes from breeding areas. The distribution of the percentage frequency of snout-vent lengths for six species of lizards suggests that individuals did not breed until their second year.

Experimental Investigation of very High Frequency Slot Antenna on M-60A-1 Tank

1977 ◽  
Author(s):  
D. V. Campbell ◽  
William Kennebeck ◽  
A. Zanella ◽  
Paul Sexton
Keyword(s):  
Experimental Investigation ◽  
High Frequency ◽  
Slot Antenna ◽  
Very High Frequency ◽  
Very High

A collision feedback based multiple access control protocol for very high frequency data exchange system in E-navigation

2021 ◽  
pp. 1-16
Author(s):  
Xu Hu ◽  
Bin Lin ◽  
Ping Wang ◽  
Hongguang Lyu ◽  
Tie-Shan Li
Keyword(s):  
Access Control ◽  
High Frequency ◽  
Multiple Access ◽  
Data Exchange ◽  
High Frequency Data ◽  
Frequency Data ◽  
Exchange System ◽  
Very High Frequency ◽  
Time Division ◽  
Very High

Abstract The very high frequency data exchange system (VDES) is promising in promoting electronic navigation (E-navigation) and improving navigation safety. The multiple access control (MAC) protocol is crucial to the transmission performance of VDES. The self-organising time division multiple access (SOTDMA) protocol, as the only access mode given by current recommendations, leads to a high rate of transmission collisions in the traditional automatic identification system (AIS), especially with heavy traffic loads. This paper proposes a novel feedback based time division multiple access (FBTDMA) protocol to address the problems caused by SOTDMA, such that collision of transmissions can be avoided in information transmission among vessels. Simulation results demonstrate that the proposed FBTDMA outperforms the traditional SOTDMA in terms of channel utilisation and throughput, and significantly reduces the transmission collision rate. The study is expected to provide insights into VDES standardisation and E-navigation modernisation.

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