Peaks Of Oscillation Research Articles

Weak dust acoustic shock wave in strongly coupled two-dimensional complex plasma

By using the equation of the state of P=αd+βdTd, we studied a shock wave propagation in a strongly coupled complex plasma. A Korteweg-de Vries–Burgers equation is obtained to describe a shock wave in strongly coupled complex plasma. Dependence of the shock wave speed on the piston velocity and the plasma parameters such as the screening parameter of the strongly coupled complex plasma are given analytically for a weak shock wave. It is in good agreement with previous results. It shows in the present paper that there are density oscillations in the postshock region which is similar to that found in the previous works. Dependence of the length between two first peaks of the density oscillation on the piston velocity and the plasma parameter are also given analytically which is also in agreement qualitatively with previous results.

Bottom-up gamma and stages of waking

Gamma activity has been proposed to promote the feed forward or “bottom-up” flow of information from lower to higher regions of the brain during perception. The pedunculopontine nucleus (PPN) modulates waking and REM sleep, and is part of the reticular activating system (RAS). The properties of PPN cells are unique in that all PPN neurons fire maximally at gamma band frequency regardless of electrophysiological or transmitter type, thus proposed as one origin of “bottom-up” gamma. This property is based on the presence of intrinsic membrane oscillations subserved by high threshold, voltage-dependent calcium channels. Moreover, some PPN cells are electrically coupled. Assuming that the population of PPN neurons has the capacity to fire at ∼40Hz coherently, then the population as a whole can be expected to generate a stable gamma band signal. But what if not all the neurons are firing at the peaks of the oscillations? That means that some cells may fire only at the peaks of every second oscillation. Therefore, the population as a whole can be expected to be firing at a net ∼20Hz. If some cells are firing at the peaks of every fourth oscillation, then the PPN as a whole would be firing at ∼10Hz. Firing at rates below 10Hz would imply that the system is seldom firing at the peaks of any oscillation, basically asleep, in slow wave sleep, thus the activation of the RAS is insufficient to promote waking. This hypothesis carries certain implications, one of which is that we awaken in stages as more and more cells are recruited to fire at the peaks of more and more oscillations. For this system, it would imply that, as we awaken, we step from ∼10Hz to ∼20Hz to ∼30Hz to ∼40Hz, that is, in stages and presumably at different levels of awareness. A similar process can be expected to take place as we fall asleep. Awakening can then be considered to be stepwise, not linear. That is, the implication is that the process of waking is a stepwise event, not a gradual increase, suggesting that the brain can spend time at each of these different stages of arousal.

Self-organization of antiperiodic oscillations

Antiperiodic oscillations forming infinite cascades of spirals were recently found experimentally and numerically in the control parameter space of an autonomous electronic circuit. They were discovered while recording one specific voltage of the circuit. Here, we show that such regular self-organization may be measured in any of the four variables of the circuit. Although the relative size of individual phases, their boundaries and the number of peaks of each characteristic oscillation depends on the physical quantity used to record them, the global structural organization of the complex phase diagrams is an invariant of the circuit. Tunable families of antiperiodic oscillations cast fresh light on new intricate behavior of nonlinear systems and open the possibility of studying hitherto unobserved phenomena.

Effect of band parameters on interband optical absorption in quantum wire structure of low band gap III–V semiconductors

A generalized theory is presented to study the effect of band parameters on inter band optical absorption in quantum wire structure of III---V compound semiconductors considering the wave-vector ( $\vec{k}$ ) dependence of the optical transition matrix element (OME). The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted to calculate the inter band optical absorption coefficient (IOAC) for a wide range of III---V compound semiconductors like, InAs, InSb, Hg1?x Cd x Te and In1?x Ga x As y P1?y lattice matched to InP, having varied split-off energy band compared to their energy band gap. It has been found that IOAC for quantum wires (QWRs) increases in oscillatory manner with increasing incident photon energy and the positions of peaks of oscillation of the coefficient are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of band energy constants. This effect of band parameters is better revealed from the study of light polarization dependence of the absorption coefficient.

Two-Terminal Spin Filter Using Quantum Dot with Spin-Orbit Interaction in Magnetic Field

We propose a two-terminal spin filter utilizing a quantum dot with spin-orbit interaction and magnetic field. First we examine a quantum dot with two energy-levels, as a minimal model, and obtain an analytical expression for the spin-dependent conductance. When the spacing between the two levels is smaller than the level broadening due to the tunnel coupling to the leads, a largely spin-polarized current is generated around the current peaks of Coulomb oscillation. Next, we perform a numerical simulation using a realistic model for a quantum dot and tunnel barriers and evaluate the efficiency of our spin filter.

Manifestation of Work Function Difference in High Order Gundlach Oscillation

Gundlach oscillation (or the standing-wave state) is a general phenomenon manifesting in the tunneling spectrum acquired from a metal surface using scanning tunneling spectroscopy. Previous studies relate the energy shift between peaks of the lowest-order Gundlach oscillation observed on the thin film and the metal substrate to the difference in their work functions. By observing Gundlach oscillations on Ag/Au(111), Ag/Cu(111), and Co/Cu(111) systems, we demonstrate that the work function difference is not the energy shift of the lowest order but the ones of higher order where a constant energy shift exhibits. Higher order Gundlach oscillations can thus be applied to determine the work function of thin metal films precisely.

Detection of spheriodal free oscillation excited by Peru 8.2 M s earthquake with five international superconducting gravimeter data

In this paper, authors obtain the spectral peaks of the earth free oscillation and check all normal modes from 0S0 to 0S48 accurately, with the Fourier analysis and the maximum entropy spectrum method dealing jointly with six groups of the observational residual data from five international superconducting gravimeter stations. By comparing the observational results in this paper with three former groups of observations or models, authors notice an extra discrepancy between two observational 0S2 modes excited separately by Peru earthquake and Alaska earthquake, which probably mirrors the anisotropy of the Earth’s inner core. The analysis on the splitting 1S2 mode shows that the asymmetric factor of rotationwise spectral splitting is possible to be different from that of anti-rotationwise spectral splitting.

Somatosensory evoked high-frequency oscillation in Parkinson's disease and myoclonus epilepsy

Aim: A high-frequency oscillation in the range of 600–900 Hz has been shown to be a component of the somatosensory evoked potential (SEP) in humans. In the present communication, we studied these oscillation potentials in two neurological disorders. Subjects and methods: Subjects were 20 healthy volunteers, 17 patients with Parkinson's disease (PD) and 3 with myoclonus epilepsy (ME). Median nerve SEPs were recorded using filters set at 0.5 and 3000 Hz. Several peaks of oscillation were obtained by digitally filtering raw SEPs from 500 to 1000 Hz, and their amplitudes and onset latencies were measured. Results: In normal subjects, several oscillation potentials were observed at the latency of 0 to 8 ms after the onset of N20. In PD patients, the oscillation potentials at normal latencies were significantly larger than those of normal subjects. Moreover, in 7 of 17 PD patients, they were extremely enlarged (>mean±3 SD of normal values). In contrast, in patients with ME, abnormally enlarged oscillation potentials were seen at longer latencies (7–14 ms) in spite of normal-sized early oscillation potentials. Magnetoencephalographic analyses showed that any oscillation potentials originated from the primary sensory cortex. Conclusions: There are at least two mechanisms for producing the oscillation potentials of SEP. Those around N20 have some relation with the basal ganglia function and are enlarged in PD patients, the others around P25-N33 are enhanced in ME patients.

Middle atmospheric ozone and temperature responses to solar irradiance variations over 27‐day periods

A one‐dimensional (1‐D), photochemical‐radiative, time‐dependent model with vertical diffusion is developed to investigate the response of ozone in the middle atmosphere to solar UV irradiance variations over 27‐day solar rotation periods. The model, based on equinoctial conditions at the equator, extends from 10 to 100 km with a vertical resolution of 0.5 km and employs an approximation based on photochemical families. The amplitudes of the wavelength‐dependent solar UV variation over 27‐day periods as observed by the Upper Atmosphere Research Satellite (UARS) are adopted in the model. The results of the 1‐D model show that at altitudes of 60–80 km, ozone decreases with increasing solar irradiance at Lyman α. The amplitude of the ozone variation is about 1% of its equilibrium value at about 70–75 km. Below 50 km an ozone increase is found due to increased photolysis of molecular oxygen by increased solar irradiance over the Herzberg continuum. The peak of this ozone increase (about 0.3%) is located at about 35 km. The peaks of the ozone oscillation in the upper stratosphere precede those of the solar oscillation as a result of the strong influence of the temperature feedback on the ozone response through the temperature dependent chemical reaction rates. A modified NCAR 2‐D model is also used to study the short‐term ozone response. Comparison of the 2‐D and 1‐D results shows that horizontal transport increases the phase lag of the temperature response. This large phase lag is essential to simulate the observed ozone response given by Nimbus 7 solar backscattered ultraviolet observations. The positive temperature response around 70 km observed by Nimbus 7 stratospheric and mesospheric sounder data is confirmed by the UARS microwave limb sounder temperature observation, but neither 1‐D nor 2‐D models are able to reproduce this observed temperature response at this level. The effects of the exothermic chemical heating and vertical diffusion coefficient on the mesospheric temperature and ozone responses are discussed. The relative response of ozone and temperature to normalized solar variations over different spectral regions and the roles of different photochemical families in the ozone response are presented. Finally, the seasonal and latitudinal (up to middle latitudes) variations in the ozone response are evaluated with the use of the 2‐D model.

How well are FREQUENCY SENSITIVITIES OF grasshopper ears tuned to species-specific song spectra?

Grasshoppers of 20 acridid species were examined using spectral analysis, laser vibrometry and electrophysiology to determine whether the song spectra, the best frequencies of tympanal-membrane vibrations and the threshold curves of the tympanal nerves are adapted to one another. The songs of almost all species have a relatively broad-band maximum in the region between 20 and 40 kHz and a narrower peak between 5 and 15 kHz. There are clear interspecific differences in the latter, which are not correlated with the length of the body or of the elytra. At the site of attachment of the low-frequency receptors (a-cells), the tympanal membrane oscillates with maximal amplitude in the region from 5 to 10 kHz. At the attachment site of the high-frequency receptors (d-cells), there is also a maximum in this region as well as another around 15-20 kHz. The tympanal nerve is most sensitive to tones between 5 and 10 kHz, with another sensitivity maximum between 25 and 35 kHz. The species may differ from one another in the position of the low-frequency peaks of the membrane oscillation, of the nerve activity and of the song spectra. No correlation was found between the characteristic frequency of the membrane oscillation and the area of the tympanal membrane. Within a given species, the frequency for maximal oscillation of the membrane at the attachment site of the low-frequency receptors and the frequency for maximal sensitivity of the tympanal nerve are in most cases very close to the low-frequency peak in the song spectrum. In the high-frequency range, the situation is different: here, the position of the peak in the song spectrum is not correlated with the membrane oscillation maximum at the attachment site of the high-frequency receptors, although there is a correlation between the song spectrum and the sensitivity of the tympanal nerve. On the whole, therefore, hearing in acridid grasshoppers is quite well adjusted to the frequency spectra of the songs, partly because the tympanal membrane acts as a frequency filter in the low-frequency range.

A Shubnikov-De Haas Study of Tilted Magnetic Field in the HgTe/CdTe Superlattice

AbstractWe have measured the Shubnikov-de Haas (SdH) effect in a HgTe/CdTe superlattice (SL) with a tilted magnetic field in the absence of an external electric field. We found that the peaks of the SdH oscillation changed with Bcosθ, indicating the two-dimensional character of the electron gas. The carrier concentration of the two-dimensional electron gas (2DEG) is equal to 2.95×1011 cm−2. The 2DEG shows the existence of a Stark ladder, which is caused by the internal electrostatic field, near the interface between the substrate and the SL. From the temperature dependence of the SdH measurements, we also show that the 3DEG in the SL miniband contributes to the non-oscillatory magnetoresistance and that the mobility of 3DEG in the miniband is lower than that of 2DEG in the Stark ladder.

Noise Spectra of a Probe in a Hot-Cathode Discharge

Measurements have been made with a floating and a biased probe of the low-frequency noise which occurs in hot-cathode discharges through mercury vapour at low pressures. As previously reported by Cobine and Gallagher, and Martin and Woods, the spectrum is continuous but there are no superimposed peaks of oscillation. The spectra agree with that of the tube noise in their general shape. It has been shown that the primary electrons from the cathode are not essential for the noise to be recorded from the probe.