Intensities Of Individual Modes Research Articles

The mode view of long-range propagation through oceanic internal waves

For long-range acoustic propagation in the ocean, calculation of internal wave effects by ray tracing is far from accurate. Full wave methods must be used. An unperturbed normal mode simulation has been developed for this case. Simulations have been carried out with a single-mode starting field, with a sound speed profile measured in the 2010 Philippine Sea experiment, and internal waves consistent with measurements at the same region and same time. Modes were chosen that turn around half way between the sound axis and the surface. The frequency is 100 Hz, appropriate for long-range propagation experiments. Ensemble averaged mode intensities are consistent with transport theory results, but the individual mode intensities as a function of range are very inconsistent with a random walk ("diffusion") in mode number space.

Generalized synchronization of chaos in identical systems with hidden degrees of freedom.

We demonstrate generalized synchronization of chaos in a two-mode laser system. The total intensity of the laser output (the sum of the individual mode intensities) is used as the drive signal. This lumped variable transmitted to the identical response system does not generate identical synchronization. Generalized synchronization is observed instead of identical synchronization because of the hidden internal degrees of freedom.

Parameters of global thunderstorm activity deduced from the long-term Schumann resonance records

Abstract Parameters of global thunderstorm activity are deduced from long-term frequency and amplitude records of the first three Schumann resonance (SR) modes performed at the Nagycennk Observatory (47.6°N, 16.7°E), Hungary, from May 1993 to May 1996. The variations of the daily frequency range of each mode, which are characteristic of the changes of the effective source width, exhibit annual and semiannual variations. Annual and semiannual variations are present in both the recorded data and the parameters of global thunderstorm activity. The effective source width varies over 3–4 h at solstices to 5–6 h during the equinox conditions. A period of about four months also appeared in the spectra of the recorded data. A similarity was found between the patterns of the annual and semiannual variations of the daily frequency range, and the changes in median solar time, apart from a three-month phase lead of the astronomical data. The similarity might be due to an unknown solar-terrestrial link. Two approaches were used for the parameterisation of the global thunderstorm activity. One of these employs the preliminary evaluation of the source-observer distance (SOD) using the ratio of individual mode amplitudes. Variations of the source intensity are obtained after dividing the amplitude recorded by that calculated for the established SOD. The second approach applies a direct summation of the individual mode intensities. Numerical simulations showed that such cumulative intensity depends on the level of the global thunderstorms rather than on the SOD. The two estimates were compared and the conclusion was made that these coincide to within ±30%. The maximum of the global thunderstorm activity occurs in summer, in the Northern hemisphere, and the minimum is observed in winter with a two-fold characteristic variance.

Temporal variations of the global lightning activity deduced from the Schumann resonance data

Temporal variations of the global lightning activity were deduced from long-term Schumann resonance (SR) continuous records. The intensities of the horizontal magnetic field component in the vicinity of the first, second, and third SR modes were monitored at Tottori observatory (35.5°N, 134.33°E) from 1968. Variations of the effective source-observer distance were estimated using the ratios of the intensities of individual modes. This allowed us to obtain average diurnal variations of the global lightning activity for each month over a one-year period. The results show that the distances estimated between the field-site and the effective source are very stable, while the temporal changes of the fields and the global lightning intensity derived demonstrate substantial variability.

Energy trends in the Japanese transportation sector

Passenger transportation in Japan, which is comprised of a high share of rail passengers and a low share of private vehicles, is considered one of the least energy-intensive transportation sectors in the industrialized countries. The thesis of this paper is that, despite low per capita energy use, when the intensities of individual modes are compared, Japanese transportation is not more energy efficient. Here, a detailed 25-year energy balance of this sector is analyzed, disaggregating fuel use within the different modes of transport as well as identifying the role of mini-cars and mini-trucks in Japanse transport activity and energy use. Changes in activity, modal structure, and modal energy intensity are separated out to describe energy-consumption trends. (Modal structure is found to be the primary factor behind the current low energy intensity of passenger transport and the high energy intensity of freight.) It is shown, through comparisons with similar data for the USA and eight European countries, that the low per capita energy use for passenger travel in Japan is related to both the low level of travel in general and the great importance of rail and bus, while there is very little difference between the structure of Japanese and European energy use for freight. The increased use of larger private cars and freight trucks continues to raise the energy intensity of the transportation sector, while air transport continues to gain shares in both sectors. Indeed, aggregate travel in Japan is more energy intensive than it is in Europe, and aggregate freight more energy intensive than in either the USA or Europe. Past improvements in energy efficiency were for the most part motivated by commercial concerns. No specific government policies to conserve transportation energy exist, and there is little evidence that policies had any effects on energy use, except, perhaps to increase energy use. The concluding discussion addresses the effects of Japanese transportation energy trends on carbon dioxide emissions.

Antiphased states in intracavity second-harmonic generation: Stability of the periodic solutions.

We study the self-pulsing solutions which emerge from the steady state via a Hopf bifurcation in a laser with intracavity second-harmonic generation. Our main result is the construction of periodic solutions and the derivation of explicit amplitude equations which rule the stability of these periodic solutions. In this way, we have been able to substantiate the classification into four classes of periodic solutions with simple phase and amplitude relations. Near the Hopf bifurcation, the periodic solutions are stable and the sum over the individual mode intensities is not periodic but constant, a signature of antiphase dynamics in this system. A fifth class of periodic solutions has been found numerically where the sum over all modal intensities is periodic. Finally, a numerical analysis complements these results and shows that the phase relations which characterize antiphase dynamics are maintained throughout the route to chaos and in the first chaotic domain when the pump parameter is increased.

Gain circulation in multimode lasers.

Self-organized collective behavior in globally coupled multimode lasers is investigated by introducing a new physical quantity, gain cirulation, that characterizes the gain transfer among lasing modes. Numerical simulations indicate that the self-organization is established such that the gain circultions in all the closed interaction paths involving arbitrary multiple lasing modes become neglibibly small as compared with direct mode-to-mode gain circulations. This implies that the nonreciprocal local (i.e., mode-to-mode) gain transfers are self-organized so as to ensure reciprocal average gain flow among modes approximately and that temporal evolutions of individual mode intensities are determined accordingly.

Instabilities and chaos in a multimode, standing-wave, cw dye laser.

Experimental and theoretical investigations of a multimode, standing-wave, cw dye laser have been carried out. The optical spectrum of the dye laser was found to evolve by discrete transitions with increasing pump power, between spectra composed of three stable modes and spectra composed of many modes whose amplitudes fluctuate strongly. The variation of the intensities versus time of individual modes of the multimode laser was measured. For pump powers where the spectrum consisted of modes with strongly fluctuating amplitudes, we found that the intensities of individual modes have a correlation time that decreases, and a variance that increases, with increasing pump power. In addition, the fluctuations were found to be deterministically chaotic. This rules out quantum noise as the origin of the fluctuations, a mechanism that had been assumed in many previous studies. We also have carried out numerical simulations of this laser, using a semiclassical model based on third-order, coupled-mode laser theory, which includes population oscillations, four-wave mixing in the gain medium, spatial hole burning, and spontaneous-emission noise. The behavior of the optical spectrum and the fluctuations of single-mode intensities are well modeled for low pump powers. The modeling indicates that four-wave mixing and spatial hole burning are responsiblemore » for the discrete transitions in the optical spectrum, and that four-wave mixing drives the strong fluctuations of the individual mode intensities.« less

Ab initiostudies on structure, vibrational spectra and infrared intensities of HCN, (HCN)2and (HCN)3

Equilibrium structure, harmonic force field and dipole moment derivatives of HCN and (HCN)2 were investigated with the aid of ab initio methods applying extended basis sets and including electron correlation at the CPF level. Vibrational spectra and infrared intensities of HCN, (HCN)2 and of several isotopically substituted species are reported. Using our previous SCF calculations on (HCN)3 as a starting point a more approximate treatment of correlation effects on structure, vibrational spectra and infrared intensities of (HCN)3 was carried out. For the linear trimer (HCN)3 we predict a structure with two nearly equal intermolecular distances in qualitative agreement with SCF results. Infrared intensities of individual modes change dramatically upon complex formation. Besides the expected increase in the intensity of C-H vibrations involved in hydrogen bonding, particularly strong intensity enhancements were observed for C≡N vibrations in the dimer and trimer in agreement with experimental data by Maronce...

Intensity autocorrelation measurements and spontaneous FM phase locking in a multimode pulsed dye laser

The intensity autocorrelation function of the output of a multilongitudinal-mode pulsed dye laser has been measured. Modeling of the results of these measurements suggests that our grazing-incidence dye laser can operate with various degrees of correlation between mode intensities and between mode phases. Two limiting types of behavior are found: When the mode intensities are correlated, the phases are random, and when the mode intensities are uncorrected, the phases are locked in an FM fashion. This result is found to be consistent with our previous study of the cross correlations between the individual mode intensities, in which we found that spatial hole burning in the standing-wave cavity influences the degree of competition and hence the degree of correlation between modes.