Relative Amplitude Of Oscillations Research Articles

Observation of low-frequency oscillation in argon helicon discharge

We present here a kind of low-frequency oscillation in argon helicon discharge with a half helical antenna. This time-dependent instability shows a global quasi-periodic oscillation of plasma density and electron temperature, with a typical frequency of a few tens of Hz which increases with external magnetic field as well as radiofrequency (RF) power. The relative oscillation amplitude decreases with magnetic field and RF power, but the rising time and pulse width do not change significantly under different discharge conditions. The oscillation can only be observed in some specific conditions of low magnetic fields and low RF power when the gas flows in from one end of the discharge area and out from another end. This global instability is suggested to be attributed to the pressure instability of neutral depletion, which is the result of compound action of gas depletion by heating expansion and gas replenishment from upstream. There are two kinds of oscillations, large and small amplitude oscillations, occurring in different discharge modes. This study could be a good verification of and complement to earlier experiments. This kind of spontaneous pulse phenomenon is also helpful in realizing a pulsing plasma source without a pulsed power supply.

SQUEEZE FILM DAMPER DYNAMIC STIFFNESS ANALYSIS, TAKING INTO ACCOUNT THE END GAP

One of the most common ways to reduce vibration in engines is the use of damping devices in the rotor supports. Damping devices may affect both the amplitude of the oscillations and the critical frequencies. The most commonly used damping devices are the squeeze film dampers (SFD), which can show dynamic stiffness that is proportional to frequency of oscillations and that is depends on the relative amplitude of oscillations. The stiffness of the damper is highly influenced by the end gap, which is also often seen as a non-contact radial clearance seal. In this work, a method is proposed that will take into account the effect of end gaps on the dynamic stiffness of a SFD. As a result of the calculations, it was found that the size of the end slots significantly affects the dynamic stiffness of a short SFD, and in some work modes it can exceed the stiffness of supports and bearings.

Perivascular pumping in the mouse brain: Improved boundary conditions reconcile theory, simulation, and experiment

Cerebrospinal fluid (CSF) flows through the perivascular spaces (PVSs) surrounding cerebral arteries. Revealing the mechanisms driving that flow could bring improved understanding of brain waste transport and insights for disorders including Alzheimer’s disease and stroke. In vivo velocity measurements of CSF in surface PVSs in mice have been used to argue that flow is driven primarily by the pulsatile motion of artery walls — perivascular pumping. However, fluid dynamics theory and simulation have predicted that perivascular pumping produces flows differing from in vivo observations starkly, particularly in the phase and relative amplitude of flow oscillation. We show that coupling theoretical and simulated flows to more realistic end boundary conditions, using resistance and compliance values measured in mice instead of using periodic boundaries, results in velocities that match observations more closely in phase and relative amplitude of oscillation, while preserving the existing agreement in mean flow speed. This quantitative agreement among theory, simulation, and in vivo measurement further supports the idea that perivascular pumping is an important CSF driver in physiological conditions.

Environmental and Circadian Regulation Combine to Shape the Rhythmic Selenoproteome.

The circadian clock orchestrates an organism’s endogenous processes with environmental 24 h cycles. Redox homeostasis and the circadian clock regulate one another to negate the potential effects of our planet’s light/dark cycle on the generation of reactive oxygen species (ROS) and attain homeostasis. Selenoproteins are an important class of redox-related enzymes that have a selenocysteine residue in the active site. This study reports functional understanding of how environmental and endogenous circadian rhythms integrate to shape the selenoproteome in a model eukaryotic cell. We mined quantitative proteomic data for the 24 selenoproteins of the picoeukaryote Ostreococcus tauri across time series, under environmentally rhythmic entrained conditions of light/dark (LD) cycles, compared to constant circadian conditions of constant light (LL). We found an overrepresentation of selenoproteins among rhythmic proteins under LL, but an underrepresentation under LD conditions. Rhythmic selenoproteins under LL that reach peak abundance later in the day showed a greater relative amplitude of oscillations than those that peak early in the day. Under LD, amplitude did not correlate with peak phase; however, we identified high-amplitude selenium uptake rhythms under LD but not LL conditions. Selenium deprivation induced strong qualitative defects in clock gene expression under LD but not LL conditions. Overall, the clear conclusion is that the circadian and environmental cycles exert differential effects on the selenoproteome, and that the combination of the two enables homeostasis. Selenoproteins may therefore play an important role in the cellular response to reactive oxygen species that form as a consequence of the transitions between light and dark.

The significance of fluorescence in transmission X‐ray absorption spectroscopy and X‐ray absorption fine structure

We present a method to explore the effect of fluorescence on X‐ray attenuation measurements obtained from X‐ray absorption spectroscopy (XAS). We use the X‐ray extended range technique‐like method (XERT‐like). The experimental setup includes different sized apertures to control the number of secondary X‐rays entering the detector. Comparison of attenuation measurements produced with different aperture combination permit investigation of the effect of fluorescence radiation. In this work, fluorescence has a large impact on the attenuation measurements of thick zinc foils. The correction is energy‐dependent and sample thickness‐dependent and changes the structure and relative amplitudes of oscillations in the near‐edge region. Correction for this systematic is important for absolute measurement, for edge‐jump and edge characterization, and for near‐edge structure and amplitudes. A significant background scattering due to zinc fluorescence from the beamline optics was identified and treated for the first time. The model theory fits the experimental measurements well. The resulting correction is most significant for thicker foils with the 50 μm sample experiencing a shift in attenuation of up to 15.5% for the largest aperture while the 25 and 10 μm samples saw corrections of up to 0.153 and 0.00639% respectively. The standard error from the dispersion and variance was reduced by up to 50.5% after the correction for the 50 μm sample. This enables high‐accuracy data and theoretical and experimental analysis to below 0.03% accuracy. The technology is advanced. There is a cost in preparation and measurement time of less than a factor of two, and the principles are clear and can be routinely implemented on any beamline. This paper focuses on the model and parameters for fluorescence.

Rationale for vacuum-pulse pump devices applied on cattle farms

One of the main elements to foster technological processes in animal husbandry are vacuumpulse pump devices designed to support dosing, mixing, transporting, lines for forage preparation and feeding, milking cows, milk processing, as well as a large number of technological processes in agriculture. The paper discusses a vacuum-pulse pumping device widely used in all industries and agriculture, a feature of which is to improve technical characteristics of the pump avoiding direct mechanical energy consumption and boasting a fairly simple design. In vacuum-pulse pumping devices, transient events are caused deliberately to increase ejection coefficient, productivity, etc. Oscillating flows of materials being transported are very diverse, due to an increased number of similarity criteria that determine flow patterns. Whereas superficial velocity and the Reynolds number are commonly used for a steady flow, for an oscillating flow, the relative frequency and the relative amplitude of oscillations are added. The objects of experimental research were ejectors with oscillating flows. The wider objective of the experiments was to determine the most effective performance indicators of the ejectors, including the degree of pressure increase, the ejection coefficient and the geometric parameter. Resulting from the experiments, a direct relationship was established between changes in the performance of a pulse-vacuum pumping device and valve material and magnitude of its oscillations. A pulse ejector is recommended to have metal-seated ball valves with a pulsation frequency of 90–100 min−1. Once applied, the proposed pulse ejector will eventually increase the transportation productivity by 14.5 %.

Effects of the Strong Ionospheric Storm of August 26, 2018: Results of Multipath Radiophysical Monitoring

A brief description of the multipath coherent radio technique installation is presented. Its goal is continuous monitoring of the dynamical processes in the ionosphere caused by space weather variations and the impact of high-energy sources in the Earth–atmosphere–ionosphere–magnetosphere system. The variations of radio-wave characteristics (the Doppler spectra and signal amplitudes) in the HF range and the ionospheric parameters over China during the ionospheric storm of August 26, 2018, are described. An ∼50–100 km ascent in the radio-wave reflection region and its oscillations with an amplitude of ∼30–40 km were observed many times during the storm on all paths. The ascents were followed by descents of the radio-wave reflection region by many tens of kilometers. The ascents and descents of the reflection region were caused by a decrease in the electron concentration by a factor of 1.5–2 and its increase by a few times, respectively. The maximal increase in the electron concentration in the E and F regions reached a factor of 1.5 and 3, respectively. The relative amplitude of oscillations in the electron concentration reached many tens of percent. The amplitude of oscillations of frequency Doppler shift was several times lower on the reference days. The observed oscillations in the frequency Doppler shift were apparently caused by generation of the atmospheric gravity waves and their subsequent propagation to the latitudes of the means of observation. The velocity of wave disturbances was ∼275–480 m/s, whereas their period was ∼60 min. The ionospheric disturbances of August 27, 2018, were insignificant despite the repeated magnetic storm.

ІНФОРМАЦІЙНО-ВИМІРЮВАЛЬНА СИСТЕМА ДЛЯ ВИЗНАЧЕННЯ АМПЛІТУДИ РЕЗОНАНСНИХ КОЛИВАНЬ ЗАКРІПЛЕНОГО ПОЛІМЕРНОГО СТРИЖНЯ НА ОСНОВІ ЦИФРОВОЇ ОБРОБКИ ТА АНАЛІЗУ ЗОБРАЖЕННЯ

For the experimental determination of the real part of the complex dynamic Young's modulus and the tangent of the mechanical loss angle of the polymeric materials, the method of shear oscillations of the fixed sample is used. The essence of the method is to measure the amplitude of the resonance oscillations of the sample, in the form of a rod when the frequency of the disturbing force changes. Based on the values of the amplitude of the transverse oscillations of the sample at different frequencies, a resonance curve is constructed, the parameters of which are the oscillation frequency and the relative amplitude. The structure of the information-measuring system for determining in real time the amplitude of the resonant oscillations of the rod in the set frequency range is presented. The determination of the amplitude of the oscillations is based on the digital processing and analysis of the image of the sample obtained by the webcam. The information management system hardware and digital image processing algorithm is implemented in the MATLAB software application using the capabilities of the graphical user environment and the NI-VISA package. The proposed sequence of operations of digital image processing which consists of capturing RGB image, converting the image to monochrome, improving the image by changing the brightness of pixels, local averaging with defined pixel window size and impulse response of the filter, border selection on the image and binarization of the image by clipping threshold of brightness. The algorithm for determining the amplitude of oscillations is based on the determination of the right and left boundaries and the linear size of the area of the binary image with pixel values equal to one relative to the vertical baseline. In addition to determining the left and right boundaries, the algorithm provides for the adjustment of the vertical baseline to the image of the sample oscillations. Based on the obtained results the possibility of constructing a resonance curve of the relative amplitudes of oscillations of the sample from the frequency of its excitation is shown.

A universal bound on excitations of heavy fields during inflation

We discuss a universal bound on any excitation of heavy fields during inflation: the ratio of the heavy field's energy density to the one driving inflation must be less than the maximally allowed relative amplitude of oscillations in the power-spectrum ρh/ρI ≲ 0.01 according to PLANCK). This bound can be traced back to the sudden change of the equation of state parameter across the excitation event.We employ a sudden transition approximation at the perturbed level, which has been used before in different settings; we check its validity by comparison to the full multi-field result in a concrete case study involving a sudden mass change of an inflaton.

Oscillations of ECR ion source beam current along the beam transport of the JYFL K-130 cyclotron

A versatile measurement system has been developed to study the temporal characteristics of ion beams in millisecond time scale. The system is composed of data acquisition hardware and LabVIEW based measurement and analysis program. The measurement system and ion beam current oscillation results measured with a 14 GHz AECR-U type ion source at University of Jyv"askyl"a, Department of Physics (JYFL), are presented. It is shown that the ion beams exhibit periodic current fluctuations at frequencies from 100 Hz to 1.5 kHz with amplitudes ranging from 1 to 65 percent of the average beam current. It is argued that these oscillations originate from the ion source plasma since their characteristics depend on the ion source tuning. It is shown that increasing the ion source solenoid magnetic field increases the relative oscillation amplitude. Increasing the ion source extraction voltage has the opposite effect. The beam current oscillations were measured along the low energy beam transport (LEBT) connecting the ion source to the JYFL K-130 cyclotron as well as in the following high energy beamline. It is shown that the beam current oscillations originating from the ion source are preserved during the LEBT but are not observed after the cyclotron. The transmission efficiency from the ion source through the cyclotron was measured with two beams of comparable beam currents but different oscillation frequency and amplitude, corresponding with the two cases typically seen when the ion source is tuned for high charge state production. The transmission of the LEBT remained unaltered but the cyclotron performance was affected by the varying oscillation characteristics.

Observations of global oscillations of the sun in the SOKOL experiment onboard the CORONAS-PHOTON satellite

The helioseismological experiment onboard the CORONAS-PHOTON satellite is intended for the study of characteristics and the internal structure of the Sun using the solar eigenmodes spectrum obtained by the measurement of fluctuations of the solar radiation intensity. This experiment is the continuation of investigations of solar global oscillations started onboard artificial satellites CORONAS-I and CORONAS-F. Measurements of fluctuations of the solar radiation intensity in seven optical ranges—from the near ultraviolet to infrared spectral regions—are carried out by the solar photometer SOKOL (SOlnechnye KOLebaniya (Solar Oscillations)) developed at IZMIRAN. Over an instrument operation period of more than 9 months, a large volume of the scientific information (more than 500 MB) has been obtained. The primary processing of obtained data was performed, and spectra of fluctuations of the solar radiation intensity were constructed. On the basis of part of the processed information obtained by the photometer SOKOL, and data of the experiment DIFOS (Differential Oscillations of the Sun) onboard the artificial satellite CORONAS-F, the dependence of the relative amplitude of oscillations on the wavelength of the observation was determined.

Thermo-oscillatory convection

Average thermal convection of an incompressible fluid performing high-frequency oscillations in a straight channel at rest is considered. It is shown that the Stokes layers play an important role in the excitation of average flows, in addition to the classical thermovibrational mechanism. Skin-layer flow generation is identified as a mechanism additional to the thermovibrational mechanism whose contribution is determined by the relative oscillation amplitude: it can have both a destabilizing and a stabilizing effect, depending on the amplitude.

Diamagnetic domains and magnetostriction in beryllium

Magnetostriction was for the first time studied under the conditions of formation of diamagnetic domains (Condon domains). Transverse magnetostriction oscillations on a beryllium single crystalline plate oriented normally to magnetic field were measured in magnetic fields up to 7 T at temperatures down to 1.5 K. The relative amplitude of oscillations increased almost as the square of magnetic field and reached 10−5. The signal had a sawtoothed shape corresponding to alternation of homogeneous and inhomogeneous (domain) states in the region of the existence of magnetic domains. The arising of domains was accompanied by singularities in the observed signals which is explained by an anomalous increase in the compressibility coefficient of the domain state: coefficient oscillations were more than 100 times larger than the value predicted by the standard theory. The observed relation between magnetization current and deformation led us to conclude that the compressibility of the metal was fully determined by conduction electrons. Magnetostriction then exactly compensated Fermi level oscillations. The position of the Fermi level therefore remained constant under magnetic field variations. In addition, the domain wall thickness had to increase as the plate grew thicker.

Ultrafast spectroscopy of wavelength-dependent coherent photoionization cross sections of Li2 wave packets in the E1Σg+ state: The role of Rydberg states

The significance of Rydberg states in the probing (via ionization) of Li2 wave packets has been studied through quantitative measurements of the relative coherent ionization cross sections in a two-color pump–probe femtosecond experiment. Following the preparation of a single intermediate rovibronic state with a cw laser, a femtosecond pump pulse (around 800 nm) creates a single two-state rotational wave packet by coherent excitation of the E1Σg+ (ν=9; J=27 and 29) states. The wave packet is then probed through ionization using time-delayed, wavelength tunable pulses (in the region 508–690 nm) while the total energy of the system is kept below the dissociation limit of Li2+. The background-free coherent ionization yield (for each probe wavelength) is measured as the relative oscillation amplitude of the single quantum beat time-dependent signal. The experimental results closely follow a relatively simple theoretical model, which is based on the assumption that the coherent ionization predominantly takes place via the excitation of high-n bound singly excited Rydberg states in the ionization continuum converging to the X 2Σg+ ground electronic state of Li2+. The best interpretation is that the high-n Rydberg states (above n∼25) undergo collisional ionization or autoionization and contribute to the measured coherent ionization signal, while the low-n Rydberg states undergo predissociation and do not contribute to the measured signal. An implication of the results is that the final states of the Li2 system, accessed by the above probe pulses, can be better approximated by a corresponding set of isolated discrete levels rather than by a continuum. This conclusion is important to experimental, as well as theoretical, coherent control and wave packet dynamics studies, in particular, when phase- and amplitude-shaped pump and probe pulses are employed. This study is also the first to investigate ionization of lithium dimer slightly below the E 1Σg+ shelf region with visible light.

Effect of perfluorochemical liquid ventilation on cardiac output and blood pressure variability in neonatal piglets with respiratory insufficiency

Respiration and mechanical ventilation induce cyclic variation in cardiac output and blood pressure. We examined these phasic hemodynamic influences of mechanical ventilation during gas ventilation and partial and tidal liquid ventilation in 7 anesthetized and paralyzed young piglets (body weight, 3.0-4.9 kg) made respiratory-insufficient by repeated saline lung lavage. Nonlinear regression analysis of cardiovascular parameters vs. time was done to quantify respiratory-induced fluctuations in hemodynamic variables. The amplitude of oscillations was expressed as a percentage of the mean hemodynamic variable during the study period, and was called the relative oscillation amplitude. The relative oscillation amplitude of left ventricular stroke volume, left ventricular output, systemic arterial pressure, and systemic perfusion pressure was significantly larger (at least twofold) during tidal liquid ventilation compared to partial liquid ventilation. No such differences were observed between gas and partial liquid ventilation at comparable gas ventilator settings. We conclude that in this animal model, within-breath modulation of left ventricular output, systemic blood pressure, and perfusion pressure was significantly increased during tidal liquid ventilation as compared to partial liquid ventilation.

Late Neogene sedimentary facies and sequences in the Pannonian Basin, Hungary

Abstract Detailed sedimentological, facies and numerical cycle analysis, combined with magnetostratigraphy, have been made in a number of boreholes in the Pannonian Basin, in order to study the causes of relative water-level changes and the history of the basin subsidence. Subsidence and infilling of the Pannonian Basin, which was an isolated lake at that time occurred mainly during the Late Miocene and Pliocene. The subsidence history was remarkably different in the individual sub-basins: early thermal subsidence was interrupted in the southern part of the basin, while high sedimentation rate and continuous subsidence was detected in the northeastern sub-basin. Three regional unconformities were detected in the Late Neogene Pannonian Basin fill, which represent 0.5 and 7.5 Ma time spans corresponding to single and composite unconformities. Consequently two main sequences build up the Late Neogene Pannonian Basin fill: a Late Miocene and a Pliocene one. Within the Late Miocene sequence there are smaller sedimentary cycles most probably corresponding to climatically driven relative lake-level changes in the Milankovitch frequency band. Considering the periods, the estimated values for precession and eccentricity in this study (19 and 370 ka) are close to the usually cited ones. In the case of obliquity the calculated period (71 ka) slightly deviates from the generally accepted number. Based on the relative amplitudes of oscillations, precession (sixth order) and obliquity (fifth order) cycles had the most significant impact on the sedimentation. Eccentricity caused cycles (fourth order) are poorly detectable in the sediments. The longer term (third order) cycles had very slight influence on the sedimentation pattern. Progradation, recorded in the Late Miocene sequence, correlates poorly in time within the basin. The dominant controls of this process probably were changes of basin subsidence rate and the very high sedimentation rate. The slow, upward trend of silt and sand bed thickness as well as that of the grain size also reflects the local progradation.

Solar cycle effect on oscillations in the period range of 2-20 days in the F region of the ionosphere

The results of Lastovicka and Mlch (1994) and Altadill and Lastovicka (1996) are extended by the use of f0F2 and h'F data from Juliusruh, Lannion and Rome. There is a strong solar cycle effect in amplitudes of oscillations in f0F2 but none or a weak solar cycle effect in relative amplitudes of oscillations in f0F2 and in amplitudes of oscillations in h'F. The conditions when the planetary wave type oscillations should be taken into account in short-term predictions and when, on the other hand, they need not be taken into account, are partly specified.

Quasi-five- and ten-day oscillations in f0F2 and their possible connection with oscillations at lower ionospheric heights

The statistical analysis of the 5-day and 10-day oscillations inferred in the upper and lower ionosphere in Central Europe from f0F2 measured in Pruhonice and the radio wave absorption in the lower ionosphere shows a remarkable degree of similarity for relative amplitudes of oscillations (not for absolute amplitudes). The relative amplitudes in both regions do not express a significant solar cycle effect and their seasonal variation is also similar except for winter. The typical relative amplitude of both 5- and 10-day oscillations in the F2-region is about 4%, which is useful information for PRIME.

Method and a simple apparatus for rapid simultaneous measurement of resonance frequency and Q factor of a quartz crystal

The quartz crystal microbalance is finding many novel uses beyond its traditional utility as a thin film deposition controller. In many situations where the quartz crystal is immersed in a viscous fluid, it is desirable to measure the crystal’s Q factor in addition to its resonance frequency. Here, we describe a simple method for simultaneous measurement of the resonance frequency, the quality factor, and the activity or relative amplitude of oscillation of a quartz crystal in vacuum and in gaseous environment. The hardware, comprising of a synthesized sine wave generator and a phase detector, passively interrogates the crystal to determine its resonance frequency and activity. The passive measurement system can detect a resonance even when the crystal is heavily damped. Representative measurement results for an AT-cut quartz crystal in a number of gases at various pressures are presented. The methodology described here may be readily applied to quartz crystals immersed in a liquid.

Cardiogenic oscillations in He and SF6 expirograms during airway and venous loading

Cardiogenic oscillations in the expired partial pressure profiles of two inert gases (He and SF6) were monitored in seven anesthetized paralyzed mechanically ventilated dogs. He and SF6 were administered either intravenously by a membrane oxygenator and partial arteriovenous bypass [venous loading (VL)] or by washin into lung gas [airway loading (AL)]. The single-breath expirograms obtained during constant-flow expiration after inspiration of test gas-free air displayed distinct and regular cardiogenic oscillations. The relative oscillation amplitude (ROA), calculated as oscillation amplitude divided by mixed expired-inspired partial pressure difference, was in the range of 1-8%. The ROA for both He and SF6 was approximately 4.2 times higher in VL than in AL, which indicated that among lung units that emptied sequentially in the cardiac cycle, the effects of alveolar ventilation-perfusion (VA/Q) inequality were more pronounced than those of alveolar ventilation-alveolar volume (VA/VA) inequality. In AL, He and SF6 oscillations were 180 degrees out of phase compared with CO2 and O2 oscillations and with He and SF6 oscillations in VL, which suggests that regions with low VA/VA had high VA/Q and very low Q/VA. The ROA was practically unaffected by breath holding in both AL and VL, which indicates that there was little diffusive or convective (cardiogenic) mixing between the lung units that were responsible for cardiogenic oscillations. The ROA was consistently higher for He than for SF6, and the He-to-SF6 ratio was independent of route of test gas loading, averaging 1.6 in both AL and VL. This result may be explained by laminar Taylor dispersion, whereby oscillations generated in peripheral lung regions are dissipated in inverse proportion to diffusion coefficient during transit through the proximal (larger) airways.