Irregular Amplitude Research Articles

Coherent two-photon absorption quenching of short laser pulses with–phaseamplitude irregularities

A phase and amplitude irregularity introduced into the spectrum of a short laser pulse by propagation through a weak narrow-line absorber results in strong suppression of continuum two-photon absorption at the peak frequency of the narrow-line absorber.

Fast type‐I waves in the equatorial electrojet: Evidence for nonisothermal ion‐acoustic speeds in the lower E region

There is plenty of evidence to suggest that the phase velocity of large amplitude irregularities produced by the modified two‐stream and the gradient‐drift instabilities are the same as the threshold speed, namely, the nominal ion‐acoustic speed in the modified two‐stream case. In this context, it is rather puzzling to note that the phase velocity of type‐I waves in the equatorial electrojet is known to easily exceed 400 m/s during strong electrojet conditions. This is puzzling because the ion‐acoustic speed of the medium is expected to be 100 m/s slower than these observations. Explaining the observations as an increase in the nominal ion‐acoustic speed through much higher neutral temperatures than expected or through electron heating by plasma waves is problematic at best. The first explanation violates everything we know about the neutral atmospheric temperature near the mesopause, while in the latter case, we only have to recall the emerging view that electron heating is done, at high latitudes, by parallel wave fields and that there is no evidence for the existence of such fields in the equatorial case. By contrast, we show that, contrary to what is normally assumed, electron thermal fluctuations cannot be neglected in the theoretical treatment of the instability when the ion collision frequency becomes large compared to the wave frequency and the wave aspect angle is small. These electron thermal fluctuations are caused by electron adiabatic heating and cooling effects related to the wave dynamics. When the electron thermal fluctuations are included in the calculations the derived instability threshold speeds match the upper limit reached by the observations. The increase becomes detectable at 108 km altitude and increases rapidly with decreasing altitude to become roughly 1.5 times as large as the isothermal ion‐acoustic speed below 100 km altitude. We show in this paper that the new threshold speed provided by the nonisothermal threshold calculations provides an excellent match for the largest vertical type‐I phase speeds that were observed during a very strong daytime electrojet event.

Assessment of nasal cycle by acoustic rhinometry and rhinomanometry

We sought to investigate the pattern, duration, and amplitude of nasal cycle and its response to nasal decongestant. Ten adult volunteers attended 2 sessions (with and without nasal spray of 0.1% xylometazoline) for consecutive examinations by rhinomanometry and acoustic rhinometry every 10 minutes over 6 hours. A spontaneous fluctuation in nasal minimum cross-sectional area, volume, and nasal resistances (inspiration and expiration) could be observed in every consecutive measurement. A significant negative correlation (r = -0.33 to -0.70, P < 0.05) between both nasal passages was shown in 5 subjects by rhinomanometry and in 2 subjects by acoustic rhinometry but was not detectable after nasal spray with 0.1% xylometazoline. A spontaneous fluctuation in nasal patency can be documented every 10 minutes with irregular pattern, frequency, and amplitude. Classic nasal cycle is not a universal phenomenon, which can be abolished by the application of decongestant.

Assessment of nasal cycle by acoustic rhinometry and rhinomanometry.

We sought to investigate the pattern, duration, and amplitude of nasal cycle and its response to nasal decongestant. Ten adult volunteers attended 2 sessions (with and without nasal spray of 0.1% xylometazoline) for consecutive examinations by rhinomanometry and acoustic rhinometry every 10 minutes over 6 hours. A spontaneous fluctuation in nasal minimum cross-sectional area, volume, and nasal resistances (inspiration and expiration) could be observed in every consecutive measurement. A significant negative correlation (r = -0.33 to -0.70, P < 0.05) between both nasal passages was shown in 5 subjects by rhinomanometry and in 2 subjects by acoustic rhinometry but was not detectable after nasal spray with 0.1% xylometazoline. A spontaneous fluctuation in nasal patency can be documented every 10 minutes with irregular pattern, frequency, and amplitude. Classic nasal cycle is not a universal phenomenon, which can be abolished by the application of decongestant.

Effect of intergranular exchange coupling on transition irregularity in coupled granular/ continuous perpendicular media

Recent simulations of coupled granular/continuous (CGC) perpendicular media are reviewed, and mechanisms previously shown to reduce bit transition irregularity are clarified using a three-dimensional micromagnetic model that includes a simple representation of grain shape irregularity. Increasing intergranular exchange coupling is found to resolve magnetic clusters at the bit transition into smaller switching units. This is shown to reduce the amplitude and cross-track correlation length of the transition irregularity. The signal-to-noise ratio (SNR) of high-density granular media and CGC media is optimized with respect to intergranular exchange coupling. Depending on the media parameters used, the recording properties of granular and CGC media are found to differ, with CGC providing greater SNR. Preliminary experimental data are presented and found to support the results obtained from simulations.

Ionic and osmotic disruptions of the lily pollen tube oscillator: testing proposed models.

Two mechanisms have been proposed as the primary control of oscillating tip growth in Lilium longiflorum Thunb. pollen tubes: changes in cell wall strength (Holdaway-Clarke et al. 1997) or alternatively, changes in turgor pressure (Messerli et al. 2000). Here we have modified the ionic and osmotic concentrations of the growth medium to test predictions derived from both models. Raising the [Ca2+]o tenfold above normal reduced the amplitude of the [Ca2+]i oscillations and growth oscillations while it raised the basal [Ca2+]i and growth rate such that the average growth rate did not change. Raising the [H+] of the growth medium tenfold reversibly decreased and sometimes eliminated the [Ca2+]i and growth oscillations without changing the average growth rate. Lowering the [H+] tenfold led to irregular frequency and amplitude [Ca2+]i oscillations, reduced the average growth rate of tubes and led to cell bursting in 33% of tubes. Addition of 50 mM H+ buffer, MES, to prevent pH changes in the cell wall increased the period, amplitude and duration of both [Ca2+]i and growth oscillations. Changing the [K+]o did not markedly effect [Ca2+]i oscillations. Reducing the osmolarity of the medium led to transient large-amplitude [Ca2+]i and growth oscillations while reducing large-amplitude oscillations over long periods. In many different conditions under which growth still occurs, lily pollen tubes maintain growth oscillations, albeit with modified frequency, amplitude and duration. We conclude that modifications to both proposed models are necessary to explain oscillating growth in this system.

A coupled oscillator model of disordered interlimb coordination in patients with Parkinson's disease.

Coordination between the left and right limbs during cyclic movements, which can be characterized by the amplitude of each limb's oscillatory movement and relative phase, is impaired in patients with Parkinson's disease (PD). A pedaling exercise on an ergometer in a recent clinical study revealed several types of coordination disorder in PD patients. These include an irregular and burst-like amplitude modulation with intermittent changes in its relative phase, a typical sign of chaotic behavior in nonlinear dynamical systems. This clinical observation leads us to hypothesize that emergence of the rhythmic motor behaviors might be concerned with nonlinearity of an underlying dynamical system. In order to gain insight into this hypothesis, we consider a simple hard-wired central pattern generator model consisting of two identical oscillators connected by reciprocal inhibition. In the model, each oscillator acts as a neural half-center controlling movement of a single limb, either left or right, and receives a control input modeling a flow of descending signals from higher motor centers. When these two control inputs are tonic-constant and identical, the model has left-right symmetry and basically exhibits ordered coordination with an alternating periodic oscillation. We show that, depending on the intensities of these two control inputs and on the difference between them that introduces asymmetry into the model, the model can reproduce several behaviors observed in the clinical study. Bifurcation analysis of the model clarifies two possible mechanisms for the generation of disordered coordination in the model: one is the spontaneous symmetry-breaking bifurcation in the model with the left-right symmetry. The other is related to the degree of asymmetry reflecting the difference between the two control inputs. Finally, clinical implications by the model's dynamics are briefly discussed.

A Nonlinear Theory for El Niño Bursting

A new mechanism is proposed that explains two key features of the observed El Niño–Southern Oscillation (ENSO) phenomenon—its irregularity and decadal amplitude changes. Using a low-order ENSO model, the authors show that the nonlinearities in the tropical heat budget can lead to bursting behavior characterized by decadal occurrences of strong El Niño events. La Niña events are not affected, a feature that is also seen in ENSO observations. One key result of this analysis is that decadal variability in the Tropics can be generated without invoking extratropical processes or stochastic forcing. The El Niño bursting behavior simulated by the low-order ENSO model can be understood in terms of the concept of homoclinic and heteroclinic connections. It is shown that this new model for ENSO amplitude modulations and irregularity, although difficult to prove, might explain some features of ENSO dynamics seen in more complex climate models and the observations.

Vocal analysis after vertical partial laryngectomy.

It is generally believed that a reconstruction of the glottic region after a vertical partial laryngectomy (VPL) can improve the glottic and supraglottic function. However, there is a paucity of reports on secondary healing without a glottic reconstruction after a VPL. The aim of this study was to obtain objective phonatory data after a VPL without a glottic reconstruction. From 1993 to 2001, 13 patients, who had been treated with VPL without a glottic reconstruction, were enrolled in this study. Patients with a postoperative follow up of less than 12 months were excluded. Seven lesions were classified as T1 glottic cancer and six as T2 glottic cancer- standard VPL (11 cases) and frontolateral VPL (2 cases). Acoustic ((fundamental frequency, Fo), jitter, shimmer, the noise to harmonic ratio (NHR)), aerodynamic (maximal phonation time (MPT), mean flow rate (MFR)) analysis and videostroboscopy were performed to evaluate the voice. There were significant differences in the Fo, jitter, shimmer, NHR, MPT and MFR between the VPL group and normal control group. In videostroboscopy, the following tendencies were observed in many cases: incomplete glottic closure, a decreased and irregular mucosal wave and amplitude, supraglottic voicing, abnormal arytenoid movement and anterior commissure blunting. Objective phonatory data after VPL without a glottic reconstruction was obtained. The voice quality after a VPL without a glottic reconstruction was somewhat unsatisfactory. A further comparison with other different surgical techniques of a VPL would help determine a better way of improving the voice quality in these patients.

An Investigation of the Irregularity of El Nino in a Coupled GCM

The irregularity of El Nino is investigated with a 400-year simulation of a coupled ocean-atmosphere general circulation model. The model produces irregular El Ninos with peak sea surface temperature (SST) anomalies ranging from 1°C to 4°C in the equatorial central-eastern Pacific. In the equatorial Pacific, the temporal phase relationship of the upper ocean heat content (OHC) anomaly relative to SST, and wind stress anomalies can be explained by the “recharge oscillator” mechanism. A difference of the zonal mean OHC anomaly between the equator and the northern subtropics arises before the development of equatorial SST anomaly. It is found that a larger OHC anomaly is accumulated on the equator as a precursor of strong El Nino. The heat-budget analysis suggests that horizontal advection in the ocean interior is a major contributor to the build-up of the larger OHC anomaly during the recharge phase, which is associated with the zonal-mean wind-curl anomaly in the off-equatorial North Pacific. This also implies that the surface heating in the subtropics is a potential contributor through meridional heat transport. Besides the aspect of amplitude irregularity, the model El Nino shows irregularities in frequency and seasonal phase locking. Possible linkages between these irregularities are discussed.

First in situ observations of equatorial ionospheric bubbles by Indian satellite SROSS‐C2 and simultaneous multisatellite scintillations

The first observation of equatorial ionospheric irregularities by RPA probe of the Indian low Earth orbiting satellite SROSS‐C2 is presented in this paper. Amplitude scintillations of medium Earth orbiting Global Positioning System (GPS) satellites and geostationary FLEETSATCOM (244 MHz, 73°E) and INMARSAT (1.5 GHz, 65°E) signals recorded simultaneously at Calcutta (lat: 22.97° N, long: 88.50°E geographic; dip: 32°N) are used for a coordinated study of equatorial F region irregularities in the Indian zone. Cases of ionospheric irregularities identified from the SROSS‐C2 records obtained during the initial one‐and‐a‐half years since its launch in May 1994 have been analyzed. Some events of in situ ion density irregularities are compared with scintillations simultaneously observed on the transionospheric satellite links. Intense bite‐outs of ion density (maximum relative irregularity amplitude ΔN/N ∼ 65%) were detected on one occasion (October 29, 1994) coupled with deep fadings (S4 ∼ 1 at VHF, ∼0.52 at L‐band, and ∼0.69 at GPS L1 frequency) on ground‐based satellite links. An estimate of scintillation indices from the observed in situ density deviations compares well with the ground‐based measurements. The development of intense equatorial bubbles even on a day like October 29, 1994, under low solar activity conditions, may be attributed to a prompt penetration of magnetospheric electric field equatorwards during the main phase of a magnetic storm in progress [maximum negative excursion of Dst ∼ −127 nT at 1600UT (2100MLT) with a dDst/dt rate −37 nT/hr at 1300–1400UT (1800–1900MLT)]. The drift velocity and spatial extent of these irregularities have been estimated from ground‐based observations.

Autogeneration of an Instability of a Plasma Composition Equilibrium in the Plasmaspheric Transition Region during a Postsunset High-Altitude Launch of the Vertikal'-10 Rocket

A cause of the instability of equilibrium of plasma ion composition is discussed and exemplified by the data on a burst of amplitudes of small-scale plasma irregularities in the plasmaspheric transition region during an evening launch of the Vertikal'-10 rocket. This burst is accompanied by a simultaneous decrease in the average plasma density at altitudes of ∼700–1100 km. Specific features of the observed events are compared to postsunset incoherent scatter radar observations of the ion diffusion flux density. It is demonstrated that the instability is caused by peculiarities of the protonosphere–ionosphere interaction associated with a sharp difference between thermal conditions of the ionospheric and protonospheric air shortly after sunset. The induced nonuniformity of postsunset cooling of the protonospheric–ionospheric plasma causes density irregularities in ion diffusion fluxes and generates local bunches of heavy ions, which are usually only a minor impurity to lighter ions. As a result, conditions are created that are favorable for the nondissipative accumulation of potential energy for the mutual opposition of two or more groups of ions with different masses and for the subsequent release of this energy by a threshold excitation of impurity-driven plasma instabilities.

Pacemaker calcium oscillations in thalamic astrocytes in situ.

During development, astrocytes in the ventrobasal thalamus display spontaneous intracellular calcium [Ca(2+)](i) oscillations, that can lead to the excitation of adjacent thalamocortical neurons via an NMDA receptor-mediated mechanism. In this study, we show that while astrocytes usually exhibit oscillations of irregular amplitude and frequency, a subset of spontaneously active thalamic astrocytes exhibits rhythmic, i.e. pacemaker, [Ca(2+)](i) oscillations with an average frequency of 0.019 Hz. This frequency of the pacemaker oscillations is close to the modal frequency of the irregularly oscillating astrocytes, suggesting that there is a preferred frequency for astrocytic [Ca(2+)](i) oscillations. If pacemaker [Ca(2+)](i) oscillations underlie excitatory signaling to neurons, the result would be rhythmic activation of thalamocortical neurons and astrocyte-driven synchronized oscillations within neurons of the thalamocortical loop.

Irregular amplitude variations and another abrupt period change in the δ Scuti star V 1162 Ori

We report that the intermediate amplitude δ Scuti star V 1162 Ori has changed its main pulsational period in the course of the year 2000. This new period change falls in a sequence of period changes observed during the last 5 years. While the average amplitude value of all our new data, 63 mmag, fits a cyclic amplitude variation suggested by Arentoft et al. (2001), splitting the data up in smaller subsets discloses significant deviations from regularity, with stretches of constant amplitude during short intervals of time. The new data show that the amplitude of one of the secondary frequencies, f2, has in 3 years dropped from more than 3 mmag to now about 1 mmag, and that the previously obtained f5 probably is a 1 d-1 alias of the real frequency. We present the newly acquired times of minimum and maximum light as support for subsequent observing campaigns.

Ionospheric irregularity diagnostics from the phase structure functions of MF/HF radio echoes

We present a new approach to investigating ionospheric irregularities, using the temporal structure function of totally reflected radio echo phase variations. Modern digital ionosondes (e.g., the dynasonde) measure the echo phase with very high resolution and precision, at closely spaced antennas, frequencies, and times. A “stringing” procedure gives continuous and unambiguous phase variation data for time intervals of any desired length. Quasi‐periods of tens of seconds up through several minutes are caused by large‐scale movements of the ionospheric plasma, while shorter‐period phase variations result from the interaction of the sounding signal with small‐scale irregularities. The relevant irregularity spatial domain extends from decameter radio wavelengths to the first Fresnel scale, a few kilometers. We obtain a theoretical relation between structure functions of the temporal phase variations and spatial irregularities with a simple model of frozen horizontal drift. The relation permits solutions of both the direct and inverse problems. Although long‐period phase measurements are practicable and essential to exploring larger irregularity scales, they require observing modes dedicated to multiple fixed‐frequency time series, and this undesirably limits the number of altitudes that can be monitored simultaneously. An alternative “rudimentary structure function” is obtainable from standard dynasonde “B‐mode” ionograms; it offers good altitude and time resolution for irregularity studies while permitting other established diagnostics (electron density profiles, vector velocities, critical frequencies, etc.) with the same data. We show some example analyses by these methods as applied to auroral and magnetic‐equatorial dynasonde observations. We find irregularity amplitudes in the range 0.001 &lt; ΔN/N &lt; 0.1 (for a nominal scale of 1 km) and spectral indices in the range 2 &lt; v &lt; 4, with evidence of diurnal variation in both quantities at both locations.

Geophysical variables and behavior: CIV. Power-frequency magnetic field transients (5 microtesla) and reports of haunt experiences within an electronically dense house.

Magnetic field measurements for power frequencies were measured continuously over two 24-hr. periods for a small house in which two adults who exhibited above normal occurrences of complex partial epileptic-like experiences had reported "waves of fear", tactile sensations, nightmares, apparitions, and a sensed presence. The experiences occurred within an area in which irregular amplitude modulations between 1 microT and 5 microT (50 mG) from 60-Hz sources, with durations of a few seconds to several tens of seconds, were measured. This case suggests that transient, complex temporal patterns of power-frequency magnetic fields generated by less than optimal grounding in dwellings and telluric currents may be sufficient to evoke experiences in the brains of sensitive individuals. Cultural labels, applied by the experients, then affect the explanations and expectancies for these experiences.

A tutorial on the basic principles of microwave reflectometry applied to fluctuation measurements in fusion plasmas

Microwave reflectometry is now routinely used for probing the structure of magnetohydrodynamic and turbulent fluctuations in fusion plasmas. Conditions specific to the core of tokamak plasmas, such as small amplitude of density irregularities and the uniformity of the background plasma, have enabled progress in the quantitative interpretation of reflectometer signals. In particular the extent of applicability of the one-dimensional (1-D) geometric optics description of the reflected field is investigated by direct comparison to 1-D full wave analysis. Significant advances in laboratory experiments are discussed which are paving the way toward a thorough understanding of this important measurement technique. Data are presented from the Tokamak Fusion Test Reactor [R. Hawryluk, Plasma Phys. Controlled Fusion 33, 1509 (1991)] identifying the validity of the geometric optics description of the scattered field and demonstrating the feasibility of imaging turbulent fluctuations in fusion scale devices.

Evaluation of the different levels of variability in the underwater light field of a shallow estuary

The underwater light climate of a shallow estuary located at the southern coast of the Baltic Sea has been investigated, with special emphasis on the spectral irradiance composition and on short-term irradiance fluctuations caused by vertical mixing and wave focussing. The inherent optical properties of the water body were dominated by phytoplankton pigment absorption in the long-wavelength range and by coloured, dissolved organic matter (cDOM) absorption in the wavelength range <500 nm, including ultraviolet-A (UV-A) and ultraviolet-B radiation (UV-B). Pronounced particulate scattering combined with the absorption values to give very high attenuation coefficients, especially for the shorter wavelengths of UV-B radiation. Photosynthetically active radiation (PAR) was found to be reduced to 1% of the surface value within 0.8 m in the inner, hypertrophic end of the estuary and within 1.9 m in the outer, eutrophic parts of this system, with corresponding 1% penetration depths for UV-B of 0.13 and 0.31 m. During late winter and early spring, the period when reduced atmospheric ozone concentrations and enhanced UV-B have been reported over northern Europe, the irradiance levels in the water column were greatly reduced, due to strong attenuation by ice cover and overlying snow. cDOM concentration of the water was also found to remain at a high level during these periods, and indeed throughout the year, thus reducing the exposure of organisms to UV-R and PAR still further. A complex irradiance regime was found in this system, with irregular and high amplitude fluctuations caused by wind-induced vertical mixing and wave focussing being superimposed upon the solar-angle-dependent seasonal and daily cycles. The methods used to quantify the short-term fluctuations are described, and their relevance to phytoplankton physiology is discussed. The wave-focussing effect is unique to the aquatic environment, and measurements showed that average subsurface irradiances could be increased by up to 5 times for periods lasting for <1 s. The highest irradiances recorded during wave-focussing events reached over 9,000 µmol photons m–2 s–1.

GEOPHYSICAL VARIABLES AND BEHAVIOR: CIV. POWER-FREQUENCY MAGNETIC FIELD TRANSIENTS (5 MICROTESLA) AND REPORTS OF HAUNT EXPERIENCES WITHIN AN ELECTRONICALLY DENSE HOUSE

Magnetic field measurements for power frequencies were measured continuously over two 24-hr. periods for a small house in which two adults who exhibited above normal occurrences of complex partial epileptic-like experiences had reported “waves of fear”, tactile sensations, nightmares, apparitions, and a sensed presence. The experiences occurred within an area in which irregular amplitude modulations between 1 microT and 5 microT (50 mG) from 60-Hz sources, with durations of a few seconds to several tens of seconds, were measured. This case suggests that transient, complex temporal patterns of power-frequency magnetic fields generated by less than optimal grounding in dwellings and telluric currents may be sufficient to evoke experiences in the brains of sensitive individuals. Cultural labels, applied by the experients, then affect the explanations and expectancies for these experiences.

Dynamic behaviors of heterogeneous flow structure in gas–solid fluidization

A method was established to quantitatively describe nonlinear dynamic behavior of heterogeneous flow structure in gas–solid fluidization by carrying out multiple resolution and time series reconstruction of experimental signals. Optimum sampling frequency was proposed by analyzing the dependence of Kolmogorov entropy of time series on sampling frequencies. Original signals could be resolved with respect first to scale, and then to time and amplitude into a periodic function and three irregular changes (micro-scale fluctuations, and meso-scale irregular amplitude and time fluctuations). Statistical analysis indicated that the three kinds of irregular components are of random characteristics, with a complicated evolution of their probability density distributions with changing operating conditions. A new distribution function, called Compound Weibull distribution with seven parameters, was developed to describe the irregular fluctuations of flow structure, leading to a nonlinear dynamic model for simulating dynamic behaviors of heterogeneous flow structure in gas–solid fluidization, which has been coded into a software package.