Low-frequency Section Research Articles

A NEW TAPERED SLOT ANTENNA WITH SYMMETRICAL AND STABLE RADIATION PATTERN

An ultra-wideband exponential tapered slot antenna with new geometrical gratings, which is fed by a nonuniform CPW- slotline balun that is essentially important for the ultra-wide band characteristic, has been introduced in this paper. The measurement shows that the frequency band is from 1.7 GHz to over 13 GHz, among which the S11 is below −10 dB except 2.35 GHz around (below −9 dB). The gratings are introduced to make the antenna to perform better radiation characteristics of a comparatively stable, symmetrical pattern and low side lobes over the operating band as well as obviously higher gain and sharper beam width in the low frequency section in comparison with the one without gratings (more than 3 dB at 1.7 GHz).

Ionic transport and localized ionic motion in Na-β′′-alumina, Na1.70Li0.32Al10.66O17

Frequency-dependent conductivities of the two-dimensional sodium-ion conductor Na-β′′-alumina, of composition Na1.70Li0.32Al10.66O17, have been taken between 100 MHz and several THz, at different temperatures. In their low-frequency sections, the spectra are affected by the polycrystallinity of the sample, i.e. by inter-grain polarization, while the vibrational component prevails in the far infrared. In a first step, these two contributions are identified and removed from the spectra. In a second step, the remaining frequency-dependent conductivities are explained in terms of the displacive movements performed by the sodium ions within the crystal volume. Here, two kinds of motion are distinguished. One is translational via vacant local residence regimes, establishing macroscopic transport. The other is localized within a residence regime. The experimental conductivities are well reproduced by model spectra. The values of the parameters used agree with the available structural information.

Attenuation of S wave in the crust of Ordos massif

We presented attenuation characteristics of S waves in the crust of Ordos massif. Using 487 pieces of digital oscillograms of 19 seismic events recorded by 32 seismologic stations located on Ordos massif and its surroundings, we have calculated the parameter of three-segment geometric attenuation and give the relation of inelastic attenuation Q value with frequency in the crust of Ordos massif, site responses of 32 stations, and source parameters of 19 events by the genetic algorithm. The results indicate that Q value (at 1 Hz) of S-wave in the crust of Ordos massif is much larger than that in the geologically active tectonic region. The site responses of the 32 stations in the high-frequency section do not show clear amplification effect except one or two stations, while in the low-frequency section, there is difference among the stations. The logarithmic value of seismic moment and the magnitude ML of 19 seismic events has a very good linear relationship.

Statistics of Fluctuations in the Solar Soft X‐Ray Emission

X-ray emission from the Sun fluctuates as a result of occasional flare events. We have calculated the power spectra of the solar soft X-ray variations using the photometric data of the GOES 6 satellite. The data cover the period 1991 September to 1994 April, about 32 months in total, and we have worked with 10 minute averages. We find that the total power spectral densities (PSDs) have three distinct components; a flat or slightly decreasing low-frequency section, a 1/f-like moderate decline medium-frequency section, and steep decline high-frequency parts. The break frequencies separating three parts are fbreak 10-4.7 Hz and 10-3.8 Hz , respectively. Such downward breaks are expected from the shot-noise (flarelike) character of solar X-ray emission, and we interpret the lower break frequency as indicating an upper limit on flare timescales. These break frequencies do not vary appreciably with activity level. This suggests the existence of a universal mechanism for triggering flares in the solar corona. Moreover, the power-law index (where we assume PSD ∝ f-β, f being frequency) of each part does not vary appreciably with the level of activity either; its average is β 0.45, 0.95, and 1.5, respectively. The overall shape of the PSD is quite similar to those of other astrophysical objects such as black hole candidate stars and active galactic nuclei, albeit on a vastly different scale.

Representation of statistical properties of wave groups for sea processes with double-peaked spectra

A method using group-induced second-order long waves(GSLW) to represent statistical properties of wave groups with double-peaked spectra is put forward in this paper on the basis of the GSLW theory. the GSLW is regarded as a weighted linear superimposition of the second-order long wave induced by the low peak frequency section and that induced by the high peak frequency section. There is a parabolic relationship between the GSLW and the wave envelope. Then the probability density function and the distribution function of the GSLW amplitude are derived. Thus the formulas for the average time duration and the mean length of runs can be derived. Good agreement between theoretical results and measured values was achieved, as verified with the measured double-peaked spectra in different regions.

Single auditory neuron response during acute acoustic trauma

By recording from single auditory neurons in the spiral ganglion of the guinea pig cochlea it was possible to monitor threshold changes to acoustic stimuli in the same neuron during acute exposures to continuous pure tones (100 dB SPL) delivered for periods of up to 180 min. Initial changes in the tuning curve were sensitivity losses at and above the characteristic frequency (CF). This asymmetric loss resuited in a shift in the CF to lower frequencies. Further exposure (up to 20 min) produced a complete loss of the sharply tuned portion of the tuning curve and the most sensitive area moved to lower frequencies by to to 0.75 of an octave when compared to the original CF. Sensitization of the low frequency section of the tuning curve could take place for short exposures (up to 20 min) but disappeared with further exposure, whether continuous or interrupted. Long term exposures (60–80 min) produced losses in the low frequency portion of the tuning curve until a point was reached when the unit no longer responded to stimuli ay 110 dB SPL.

Abnormally low electromagnetic scattering cross sections*

We discuss the possibility of achieving abnormally low electromagnetic scattering cross sections at low frequencies by adjusting the optical properties of the scatterers (e.g., concentric spheres), generalizing the work in an earlier communication. The discussion is based upon an expansion valid for any spherical scatterer of finite size and is model independent. It is shown that if the electric and magnetic dipole scattering lengths are made to vanish, the low-frequency cross section is proportional to k8 for dielectric bodies, as has been observed experimentally in phase-separated glasses and in precipitated alloys. The angular distribution under these conditions is discussed, and is found normally to peak in the backward direction also in agreement with experiment.

Trough waveguide dual-frequency antenna

A new type of dual-frequency antenna using a hollow-fin trough waveguide is described. The hollow fin is used as a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TE_{10}</tex> mode waveguide with sidewall radiating elements. These Sidewall radiating elements constitute the high-frequency section of the antenna. The low-frequency section consists of a thick hollow-fin trough waveguide antenna. The attenuation due to radiation and waveguide wavelength of the trough waveguide section are analyzed. This analysis shows good agreement with experimental measurements. Existing data may be used as a guide in the design of the high-frequency section of this antenna, and the data presented may be used as a guide in the design of the low-frequency section.

Boundary layer near the surface of a solid body and low-frequency dielectric dispersion

The paper deals with the possibility of studying the stagnant part of the boundary layer on the basis of effects due to polarization of the electrochemical double layer (DL). A theory is developed for polarization of the diffuse part of a thin DL of a spherical particle in a direct and alternating field, allowing for the effect of ion flow through the stagnant part of the DL. Formulae are obtained on the basis of this theory for electrophoresis complicated by polarization and for the large low-frequency dielectric dispersion (ω). Calculation of the stagnant layer thickness and the ionic mobilities of this layer is shown to be possible on the basis of electrophoretic measurement on three fractions of spherical particles with identical values of ψd and ζ. Using only one fraction, we can obtain similar information from the low-frequency section of (ω).

Complete night of vertical-incidence ionosphere soundings covering frequency range from 50 kc/s to 25 Mc/s

The readers of this Journal will be interested in seeing the Figure on the following page. It is the first presentation, to my knowledge, of a group of vertical-incidence ionosphere soundings covering the entire frequency range from below 100 kc/s to 25 Mc/s. Each record is a composite made by joining at the 2-Mc/s marker one record made by a standard Model C-4 recorder and a record made at approximately the same time by the experimental low-frequency recorder in use at the Sunset Field Station, about 15 miles distant. The series shown includes a complete night with sunset and sunrise at half-hour intervals. Enlargements were made to secure an approximate match of the virtual-height scales. As one can see, the low-frequency section is made with a linear frequency sweep, and the high-frequency part uses the logarithmic scale.