Fundamental properties of surface waves in lossless stratified structures

2010 ◽  
Vol 466 (2120) ◽  
pp. 2447-2469 ◽  
Author(s):  
Guido Valerio ◽  
David R. Jackson ◽  
Alessandro Galli
Keyword(s):  
Surface Waves ◽  
Dispersion Equation ◽  
High Frequency ◽  
Low Frequency ◽  
Layered Structures ◽  
Graphical Solution ◽  
Fundamental Properties ◽  
The Past ◽  
Permittivity And Permeability ◽  
Constitutive Parameters

This paper is focused on dispersive properties of lossless planar layered structures with media having positive constitutive parameters (permittivity and permeability), possibly uniaxially anisotropic. Some of these properties have been derived in the past with reference to specific simple layered structures, and are here established with more general proofs, valid for arbitrary layered structures with positive parameters. As a first step, a simple application of the Smith chart to the relevant dispersion equation is used to prove that evanescent (or plasmonic-type) waves cannot be supported by layers with positive parameters. The main part of the paper is then focused on a generalization of a common graphical solution of the dispersion equation, in order to derive some general properties about the behaviour of the wavenumbers of surface waves as a function of frequency. The wavenumbers normalized with respect to frequency are shown to be always increasing with frequency, and at high frequency they tend to the highest refractive index in the layers. Moreover, two surface waves with the same polarization cannot have the same wavenumber at a given frequency. The low-frequency behaviours are also briefly addressed. The results are derived by means of a suitable application of Foster’s theorem.

The spatio-temporal characteristics of forest fires in China: observations from hybrid remote sensing data

2020 ◽  
Author(s):  
Lei Fang ◽  
Zeyu Qiao ◽  
Jian Yang
Keyword(s):  
Forest Fire ◽  
Forest Fires ◽  
High Frequency ◽  
Fire Management ◽  
Hot Spot ◽  
Landsat Imagery ◽  
Low Frequency ◽  
Burned Area ◽  
Prevention Policy ◽  
The Past

<p>Forest fire is a natural disaster threatening global human well-beings as well as a crucial disturbance agent driving forest landscape changes. The remotely sensed burned area (BA) products can provide spatially and temporally continuous monitoring of global fires, but the accuracies remain to be improved. We firstly developed a hybrid burned area mapping approach, which integrated the advantages of a 250 m global BA product (CCI_Fire) and a 30 m global forest change (GFC) product, to generate an improved 250 m BA product (so-called CCI_GFC product). Based on 248 fire patches derived from Landsat imagery, the results showed that the CCI_GFC product improved the CCI_Fire product substantially, which are significantly better than MCD64A1 product. According to the CCI_GFC, we found the total BA in the past 17 years was about 12.1 million ha in China, which approximately covered 6.1% of the total forested areas with a significantly decreased trend through Mann-Kendall test (Tau= -0.47, P<0.05) . We conducted a grid analysis (0.05°×0.05°) to determine the hot spots of forest fire from 2001 to 2017. We also quantified fire characteristics on frequency, spatial distribution, and seasonality in terms of Burned Forest Rate (BFR), hot spot areas, and fire seasons, respectively. We found that low frequency burns with a 0<BFR≤20% in 17 years covered 64% of total grids; the medium-low frequency burns (20%<BFR≤40%), the medium frequency burns (40%<BFR≤60%), the medium-high frequency burns (60%< BFR≤80%) accounted for 15%, 7%, 4% respectively; the high frequency burns (80%<BFR≤100%) and extremely high burns (100%<BFR≤120%) together occupy 10% of total grids which mainly distributed in Xiao Hinggan mountains, south China, and southwest China. The seasonality of forest fires differed substantially among eco-regions. The fire seasons of two temperate forest eco-regions are spring and autumn. The two peak fire months are May and October, in which about 22% and 37% of the total burned area were founded respectively. As a comparison, fire seasons in tropical and subtropical eco-regions are spring and winter (i.e., November to March of the next year), which accounted 88% of the total burned area. Our study clearly illustrated the characteristics of forest fire patterns in the past 17 years, which highlighted the remarkable achievements due to a nationwide implementation of fire prevention policy. At the same time, we emphasized that it is critically important to regard the long-term forest fire dynamics to design scientific and reasonable strategies or methods for fire management and controlling, which will be of sound significance to optimize the allocation of financial resources on fire management, and to achieve sustainable management of forests.</p>

scholarly journals The Influence of Word Retrieval and Planning on Phonetic Variation: Implications for Exemplar Models

2015 ◽  
Vol 1 (1) ◽  
Author(s):  
Angela Fink ◽  
Matthew Goldrick
Keyword(s):  
High Frequency ◽  
Empirical Studies ◽  
Low Frequency ◽  
Word Retrieval ◽  
Phonetic Variation ◽  
Exemplar Models ◽  
The Past ◽  
Single Mechanism ◽  
High Frequency Words

AbstractOver the past several decades, an increasing number of empirical studies have documented the interaction of information across the traditional linguistic modules of phonetics, phonology, and lexicon. For example, the frequency with which a word occurs influences its phonetic properties of its sounds; high frequency words tend to be reduced relative to low frequency words. Lexicalist Exemplar Models have been successful in accounting for this body of results through a single mechanism,

Nonlinear interaction of electrostatic surface waves in a semi-infinite plasma. Part 1. Derivation of the coupled mode equations

1981 ◽  
Vol 26 (2) ◽  
pp. 217-230 ◽  
Author(s):  
V. Atanassov ◽  
R. Mateev ◽  
I. Zhelyazkov
Keyword(s):  
Surface Waves ◽  
Nonlinear Interaction ◽  
High Frequency ◽  
Low Frequency ◽  
Density Perturbation ◽  
Coupled Mode ◽  
Hybrid Nature ◽  
Bulk Waves ◽  
Amplitude Attenuation

We have derived a set of coupled mode equations which govern the nonlinear interaction of three high-frequency electrostatic surface waves through a low-frequency density perturbation produced by them. The set is compared with that obtained when a similar problem is solved for bulk waves in an infinite plasma. Some differences are shown to exist caused by the specific features of surface waves such as the amplitude attenuation normal to the interface and their hybrid nature.

Nonlinear interaction of electrostatic surface waves in a semi-infinite plasma. Part 2. Time-dependent solutions to the coupled mode equations

1981 ◽  
Vol 26 (2) ◽  
pp. 231-252 ◽  
Author(s):  
V. Atanassov ◽  
E. Mateev ◽  
I. Zhelyazkov
Keyword(s):  
Surface Waves ◽  
Nonlinear Interaction ◽  
High Frequency ◽  
Low Frequency ◽  
Density Perturbation ◽  
Time Dependent ◽  
Opposite Case ◽  
Coupled Mode ◽  
Wave Resonance ◽  
Parametric Approximation

The coupled mode equations which govern the nonlinear interaction of three electrostatic high-frequency surface waves and a low-frequency density perturbation are analysed considering time-dependent solutions only. We show the existence of a filamentation instability in the static limit for the low-frequency density perturbation. In the opposite case (density perturbation close to the lowfrequency surface wave resonance) we arrive at a decay instability where only surface waves take part. The parametric approximation (growth rate and threshold) as well as the nonlinear evolution of both types of instabilities are studied.

RADIATION FROM A SOURCE NEAR A PLANE INTERFACE BETWEEN AN ISOTROPIC AND A GYROTROPIC DIELECTRIC

1964 ◽  
Vol 42 (11) ◽  
pp. 2153-2172 ◽  
Author(s):  
S. R. Seshadri ◽  
A. Hessel
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Field ◽  
Surface Waves ◽  
High Frequency ◽  
Free Space ◽  
Line Source ◽  
Low Frequency ◽  
Plane Interface ◽  
Magnetic Current ◽  
Asymptotic Evaluation

The radiation from a line source of magnetic current situated in free space near a plane interface between a semi-infinite free space and a semi-infinite gyrotropic dielectric is investigated for the case in which the gyrotropic axis is parallel to the line source. In addition to the space waves, it is found that in general two unidirectional surface waves are excited along the interface. The dispersion relations for the space and the surface waves are thoroughly examined. Both surface waves have different high-frequency cutoff but no low-frequency cutoff. The characteristics of these surface waves are investigated. An asymptotic evaluation of the total electromagnetic field is carried out for a particularly simple choice of the source frequency. For this frequency, the dependence of the efficiency of excitation of the surface waves on the distance of the source from the interface is determined. The radiation patterns are plotted for various values of the static magnetic field and the position of the source.

scholarly journals A TISSUE CULTURE APPROACH FOR DEVELOPING TETRAPLOID WATERMELONS

HortScience ◽  
1996 ◽  
Vol 31 (5) ◽  
pp. 747b-747
Author(s):  
Xingping Zhang ◽  
Billy B. Rhodes
Keyword(s):  
Tissue Culture ◽  
High Frequency ◽  
Shoot Organogenesis ◽  
Leaf Shape ◽  
Low Frequency ◽  
Female Fertility ◽  
Leaf Margin ◽  
The Past ◽  
Colchicine Solution ◽  
Seed Characteristics

Tetraploids are needed to synthesize triploid watermelons, which produce “seedless” fruit with improved quality. Traditionally, the tetraploids are induced by applying colchicine to the growing apex of seedlings or soaking the seeds with colchicine solution. This method often produces low frequency of tetraploids and high frequency of chimeras. Breeding tetraploids takes much longer time than breeding diploids because of the low female fertility. We developed a tissue culture approach that allows breeders to develop desirable tetraploids with commercially acceptable volume of seed in 2 years. This tissue culture approach includes: 1) regenerate plants via shoot organogenesis from cotyledon tissue; 2) screen tetraploids based on leaf morphology (more serrated leaf margin and wider leaf shape) before transplanting, and confirm tetraploids based on pollen morphology (larger pollen with four copi) and/or seed characteristics; 3) self-pollinate tetraploids or cross the tetraploids with diploids to accurately estimate the female fertility; 4) micropropagate the best tetraploid(s) using axillary buds during the off-season; and 5) produce tetraploid seed from the cloned tetraploids in an isolation plot and evaluate the triploids derived from the tetraploid(s) in the following season. This approach has been practiced on more than 20 genotypes over the past 4 years.

scholarly journals Experimental studies of surface waves inside a cylindrical container

2011 ◽  
Vol 677 ◽  
pp. 39-62 ◽  
Author(s):  
CUNBIAO LEE ◽  
HUAIWU PENG ◽  
HUIJING YUAN ◽  
JIEZHI WU ◽  
MINGDE ZHOU ◽  
...  
Keyword(s):  
Surface Waves ◽  
High Frequency ◽  
Experimental Studies ◽  
Low Frequency ◽  
Capillary Waves ◽  
Physical Processes ◽  
Vortex Streets ◽  
Circular Capillary ◽  
Particle Imaging ◽  
Azimuthal Waves

We experimentally investigate the dynamics of surface waves excited by oscillations from a cylindrical sidewall. Particle-imaging-velocimetry measurements with fluorescent particles were used to determine the flow patterns near the sidewall of the cylindrical fluid container and to identify the locations of the evolving air–water interfaces. The high-frequency wall oscillations created four jets that originate at the cylindrical sidewall. Four vortex streets shed from the jets propagate from the sidewall to the centre of the container and subsequently excite a low-frequency gravity wave. The interaction between this gravitational surface wave and the high-frequency capillary waves was found to be responsible for creating droplet splash at the water surface. This phenomenon was first described as ‘Long-Xi’ or ‘dragon wash’ in ancient China. The physical processes for generating the droplet ejection, including the circular capillary waves, azimuthal waves, streaming jets and low-frequency gravity waves, are described in this paper.

scholarly journals The UTR-2 Very Low Frequency Sky Survey and Its Main Results

1998 ◽  
Vol 179 ◽  
pp. 100-102
Author(s):  
K.P. Sokolov
Keyword(s):  
High Frequency ◽  
Surface Brightness ◽  
Low Frequency ◽  
Source Population ◽  
Low Frequencies ◽  
Physical Conditions ◽  
The Past ◽  
Sky Survey ◽  
Low Surface Brightness ◽  
Compact Sources

During the past decade there has been a dramatic increase in the amount of high-frequency (v > 1000 MHz) data currently underlying the studies of bright compact sources (Tb ∼ 1011–12K, l ≤ 1 kpc) with flat spectra. But in order to determine physical conditions inside extragalactic radio sources at different stages of their evolution the studies of old extended (l ∼ 100 kpc) sources with low surface brightness and steep spectra which constitute the dominant radio source population at very low frequencies (v ≪ 100 MHz) are also needed. These sources are known to represent the final stage in the evolution of extragalactic objects.

scholarly journals The Generation of ULF/ELF/VLF Waves in the Ionosphere by Modulated Heating

Universe ◽  
2021 ◽  
Vol 7 (2) ◽  
pp. 29
Author(s):  
Zhe Guo ◽  
Hanxian Fang ◽  
Farideh Honary
Keyword(s):  
High Frequency ◽  
Modulation Frequency ◽  
Source Region ◽  
Low Frequency ◽  
Future Research ◽  
Very Low Frequency ◽  
The Past ◽  
Ionospheric Modification ◽  
Vlf Waves ◽  
Scientific Achievements

One of the most important effects of ionospheric modification by high power, high frequency (HF) waves is the generation of ultra low frequency/extremely low frequency/very low frequency (ULF/ELF/VLF) waves by modulated heating. This paper reviews the scientific achievements of the past five decades regarding the main mechanisms of excitation of ULF/ELF/VLF waves and discusses their characteristics, such as their electrojet dependency, the location of the source region, continuous and discontinuous waves, the number of HF arrays, and the suitable range of the modulation frequency for different proposed mechanisms. Finally, the outlook for future research in this area is presented.

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