Long-period Oscillations Research Articles

Repetitive shock waves generated by a single long pulse underwater arc discharge

The electrohydraulic effect induced by underwater arc discharge is an efficient way to generate controllable, high-intensity shock waves. However, the development process of underwater arc discharge involves the complex coupling of plasma arc, gas bubble, and liquid medium, of which the evolution mechanism is not well understood. In this paper, the underwater arc discharge process at a millisecond pulse (>50 ms) was investigated by high-speed shadow imaging and colorimetric temperature measurement, and a simulation model of bubble pulsation was proposed to quantitatively estimate the state variation and energy transfer of the gas bubble. The results indicate that the whole arc discharge process can be categorized into three successive stages: short-period oscillation, long-period oscillation, and quasi-steady state. The vapor inside the bubble can reach a supercritical state (827 K and 140 MPa) at the minimum bubble radius. The simulation shows that the light radiation absorption and the heat conduct loss through metal electrodes are the two dominant factors influencing the pulsation of the bubble, and further analysis indicates that the dynamic evolution of the arc determines the bubble pulsation mode. Our findings demonstrate why and how repetitive electrohydraulic shock waves can be generated by a single long pulse underwater arc discharge, providing a low-cost way of shock wave generator based on an AC/DC high-voltage power source.

Statistical Investigation of Wave Propagation in the Quiet-Sun Using IRIS Spectroscopic Observations

In this analysis, we use spectroscopic observations of the quiet Sun made by the IRIS instrument and investigate wave propagation. We analyze various spectral lines formed in different atmospheric layers, such as the photosphere, chromosphere, and transition region. We examine the Doppler velocity time series at various locations in the quiet Sun to determine the dominant oscillation periods. Our results executing statistical analysis resemble those of the classical physical scenario, indicating that the photosphere is mainly characterized by the dominant 5 minute period, while the chromosphere is primarily associated with the 3 minute oscillation period. In the transition region, we observe a variety of oscillation periods, with dominant periods of 3, 8, and 12 minutes. We estimate the cutoff frequency by deducing the phase difference between two Doppler velocity time series obtained from spectral line pairs in different atmospheric layers formed at different temperatures. This reveals a significant correlation between 3 minute periods in the transition region and photospheric oscillations, suggesting that these oscillations in the transition region might propagate from the photosphere. Additionally, we analyze the phase difference between chromospheric oscillations and photospheric oscillations, demonstrating that only the 3 minute oscillations propagate upward. Based on the statistical analyses, we suggest the presence of magnetoacoustic waves in the solar atmosphere, some of which are propagating from the lower solar atmosphere upward, while some others are propagating downward. The transition region carries both long-period oscillations generated in situ and some photospheric oscillations that are also able to reach there from below.

Long-period oscillations in the lower solar atmosphere prior to flare events

Multiple studies have identified a range of oscillation periods in active regions, from 3-5 minutes to long-period oscillations that last from tens of minutes to several hours. Recently, it was also suggested that these periods are connected with eruptive activity in the active regions. Thus, it is essential to understand the relation between oscillations in solar active regions and their solar eruption activity. We investigate the long-period oscillations of NOAA12353 prior to a series of C-class flares and correlate the findings with the 3- to 5-minute oscillations that were previously studied in the same active region. The objective of this work is to elucidate the presence of various oscillations with long periods in the lower solar atmosphere both before and after the flare events. To detect long-period oscillations, we assessed the emergence, shearing, and total magnetic helicity flux components from the photosphere to the top of the chromosphere. To analyze the magnetic helicity flux in the lower solar atmosphere, we used linear force-free field extrapolation to construct a model of the magnetic field structure of the active region. Subsequently, the location of long-period oscillations in the active region was probed by examining the spectral energy density of the measured intensity signal in the 1700\,AA , 1600\,AA , and 304\,AA channels of the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO). Significant oscillation periods were determined by means of a wavelet analysis. Based on the evolution of the three magnetic helicity flux components, 3- to 8-hour periods were found both before and after the flare events, spanning from the photosphere to the chromosphere. These 3- to 8-hour periods were also evident throughout the active region in the photosphere in the 1700\,AA channel. Observations of AIA 1600\,AA and 304\,AA channels, which cover the chromosphere to the transition region, revealed oscillations of 3-8 hours near the region in which the flare occurred. The spatial distribution of the measured long-period oscillations mirror the previously reported distribution of 3- to 5-minute oscillations in NOAA12353 that were seen both before and after the flares. This case study suggest that the varying oscillation properties in a solar active region could be indicative of future flaring activity.

Temporal dynamics of surface phonon polaritons in polar dielectric nanoparticles with nonlocality

Surface phonon polaritons (SPhPs) supported by polar dielectrics have been a promising platform for nanophotonics in mid-infrared spectral range. In this work, the temporal dynamic behavior of polar dielectric nanoparticles without (or with) spatial dispersion/nonlocality driven by the ultrashort Gaussian pulses is carried out. We demonstrate that three possible scenarios for the temporal evolutions of the dipole moment including ultrafast oscillations with the decay, exponential decay, and keeping a Gaussian shape exist, when the pulse duration of the incident field is much shorter than, similar to, and much longer than the localized SPhP lifetime. Once the nonlocal effect is considered, the oscillation period becomes large slightly, and the exponential decay turns fast. Furthermore, nonlocality-induced novel temporal behavior is found such as the decay with long-period oscillations when the center frequency of the incident pulse lies at the frequency of adjacent longitudinal resonant modes. The positive and negative time-shifts of the dielectric response reveal that the excitation of the dipole moment will be delayed or advanced. These temporal evolutions can pave the way towards potential applications in the modulation of ultrafast signals for the mid-infrared optoelectronic nanodevices.

Forced air oscillations - pneumatic capacitance in microfluidic oscillators produces non-linear responses and emergent behaviors.

Pneumatic control mechanisms have long been integral to microfluidic systems, primarily using solenoid valves, pressurized gases, and vacuums to direct liquid flow. Despite advancements in liquid-driven self-regulated microfluidic circuits, gas-driven systems leveraging fluid compressibility remain underexplored. This study presents a mathematical and experimental investigation of gas-driven microfluidic circuits, focusing on forced-air oscillators. We derive and validate a first-principles model of microfluidic circuit elements operated under positive pressurization, using a 'molecular packets' analogy to elucidate compressibility effects. Our findings reveal that gas compressibility impacts circuit behavior, by acting similar to a large capacitor in the system, which inherently results in longer oscillation periods. As the syringe evacuates, the capacitance decreases, which in turn reduces the oscillation period. Experimental validation of our system demonstrates persistent behavior when using forced air to drive the microfluidic oscillators, this includes assessing devices with various PDMS membrane thicknesses, as well as evaluating device performance under different flow rates and syringe sizes. The forced air oscillators exhibited decreasing periods and capacitance over time, aligning with our theoretical predictions.

Evolution of Negative Superhumps, Quasiperiodic Oscillations, and Outbursts in the Z Cam-type Dwarf Nova AH Her

AH Her is a Z Cam-type dwarf nova with an orbital period of ∼0.258 days. Dwarf nova oscillations and long-period dwarf nova oscillations have been detected, but no quasiperiodic oscillations (QPOs) and negative superhumps (NSHs) have been found. We investigated the association between NSHs, QPOs, and outbursts of AH Her based on Transiting Exoplanet Survey Satellite photometry. We find for the first time NSHs with a period of 0.24497(1) days in AH Her, and trace the variation in the amplitude and period of NSHs with the outburst. The amplitude of the NSHs is the most significant at quiescence, weakening as the outburst rises, becoming undetectable at the top, rebounding and weakening at the plateau, and strengthening again as the outburst declines. The variation in the accretion disk radius can explain the NSH amplitude variation except for the plateau, so we suggest that the relationship between the NSH amplitude and outburst can be used as a window to study the accretion disk instability and the origin of NSHs. In addition, we find periodic variations in the amplitude, maxima, and shape of the NSHs ranging from 2.33(2) to 2.68(5) days, which may be related to the precession of the tilted disk. Finally, we find QPOs at the top of AH Her’s long outburst with ∼2800 s similar to those of HS 2325+8205, suggesting that the presence of QPOs at the top of Z Cam’s long outburst may be a general phenomenon.

Long-term variations in the mesopause region derived from OH*(3,1) rotational temperature observations at Wuppertal, Germany, from 1988 – 2022

We analysed the time series of OH*(3,1) rotational temperatures observed from Wuppertal in the time interval 1988 – 2022. The long-term evolution of the time series is characterised by two components. Firstly, we derived a significant correlation of the temperatures and the F10.7 cm solar radio flux. The sensitivity to the 11-year cycle of solar activity is 4.8 ± 0.7 K (100SFU)−1. Then we show that the second major component in addition to this solar influence is a significant long-period oscillation. The oscillation has a period of P = 22.2 ± 1.5 years with an amplitude of A = 1.8 ± 0.4 K. A significant linear trend cannot be derived for the time series of OH*(3,1) rotational temperatures. Due to the long-period oscillation the derivation of linear trends heavily depends on the analysed time interval. This explains the different linear trends that have been derived in past studies for this time series. All of the previous results for this quantity are in good agreement with the long-period oscillation determined here, because different parts of the time series and, therefore, different parts of the oscillation (e.g mainly downswing or a complete cycle) have been analysed which led to largely different linear trends.

Complex Dynamics Modes in a Simple Model of Prey-Predator Community: Bistability and Multistability

The paper proposes and studies a two-component discrete-time model of the prey-predator community considering zooplankton and fish interactions and their development features. Discrete-time systems of equations allow us to take into account naturally the rhythm of many processes occurring in marine and freshwater communities, which are subject to cyclical fluctuations due to the daily and seasonal cycle. We describe the dynamics of fish and zooplankton populations constituting the community by Ricker’s model, which is well-studied and widely used in population modeling. To consider the species interaction, we use the Holling-II type response function taking into account predator saturation. We carried out the study of the proposed model. The system is shown to have from one to three non-trivial equilibria, which gives the existence of the complete community. In addition to the saddle-node bifurcation, which generates bistability of stationary dynamics, a nontrivial equilibrium loses its stability according to the Neimark-Sacker scenario with an increase in the reproductive potential of both predator and prey species, as a result of which the community exhibits long-period oscillations similar to those observed in experiments. With the higher bifurcation parameter, the reverse Neimark-Sacker bifurcation is shown to occur followed by the closed invariant curve collapses, and dynamics of the population stabilizes, later losing stability through a cascade of period-doubling bifurcations. Multistability complicates the birth and disappearance of the invariant curve in the phase space scenario by the emergence of another irregular dynamics in the system with the single unstable nontrivial fixed point. At fixed values of the model parameters and different initial conditions, the system considered is shown to demonstrate various quasi-periodic oscillations. Despite extreme simplicity, the proposed discrete-time model of community dynamics demonstrates a wide variety and variability of dynamic modes. It shows that the influence of environmental conditions can change the type and nature of the observed dynamics.

Spatial habitat heterogeneity influences host-pathogen dynamics in a patchy population of Ranchman's tiger moth.

Host-pathogen dynamics are influenced by many factors that vary locally, but models of disease rarely consider dynamics across spatially heterogeneous environments. In addition, theory predicts that dispersal will influence host-pathogen dynamics of populations that are linked, although this has not been examined empirically in natural systems. We examined the spatial dynamics of a patchy population of tiger moths and its baculovirus pathogen, in which habitat type and weather influence dynamics. Theoretical models of host-baculovirus dynamics predict that such variation in dynamics between habitat types could be driven by a range of factors, of which we predict two are likely to be operating in this system: (1) differences in the environmental persistence of pathogens or (2) differences in host intrinsic rates of increase. We used time series models and monitored infection rates of hosts to characterize population and disease dynamics and distinguish between these possibilities. We also examined the role of host dispersal (connectivity) and weather as important contributors to dynamics, using time series models and experiments. We found that the population growth rate was higher, delayed density dependence was weaker, and long-period oscillations had lower amplitudes in high-quality habitat patches. The infection rate was higher on average in high-quality habitat, and this was likely to have been driven by higher mean population densities and no differences in pathogen persistence in different habitats (delayed density dependence). Time series modeling and experiments also showed an interactive effect of temperature and precipitation on moth population growth rates (likely caused by variation in host plant quality and quantity), and an effect of connectivity. Our results showed that spatial heterogeneity, connectivity, climate, and their interactions were important in driving host-baculovirus dynamics. In particular, our study found that connected patches and spatial heterogeneity generated differences in dynamics that only partially aligned with theoretical predictions.

Chronobiological aspects of the anti-stress effect of anxiolytics

BACKGROUND: A stressful event, being a disturbing factor, is invariably accompanied by the disorganization of biological rhythms.
 AIM: To examine the effects of stress and pharmacological substances on two models of the temporal organization of behavior, i.e., circadian locomotion and swimming dynamics in rats.
 MATERIALS AND METHODS: The daily dynamics of rat mobility were assessed in a specially designed device consisting of living cells connected to a computer. Each cell is connected by a lever and a hinge with a button. When the rat moved from one end of the box to the other, the contact was closed, and the program autonomously summed up the number of such movements for each hour of the experiment. The total number of transitions was counted in 3 h, followed by the construction of a chronogram of the circadian rhythm of mobility. To assess the effect of substances on the circadian rhythm, anxiolytics diazepam (0.1 mg/kg), tofisopam (10 mg/kg), and epiphyseal hormone melatonin (0.1 mg/kg) were injected intraperitoneally into rats. Rats that received the same volume of saline injections (0.5 mL) served as controls.
 RESULTS: Substances with anxiolytic properties, benzodiazepine derivatives diazepam (0.1 mg/kg) and tofisopam (10 mg/kg), and epiphyseal hormone melatonin (0.1 mg/kg), similarly eliminated stress-induced dysrhythmia in rats. Under their influence, the circadian rhythm of motor activity was normalized, and adaptive shifts were observed in the temporal dynamics of forced swimming.
 CONCLUSION: A single stressful event disrupts the dynamics of daily mobility in rats. Diazepam, tofisopam, and melatonin, while differing in potency, generally alleviate these disorders. In particular, anxiolytics restore the rhythm in animals highly sensitive to stress. The studied substances reorganized the temporal dynamics in rats subjected to forced swimming and increased the proportion of long-period oscillations. Primary or secondary elimination of stress dysrhythmia is an important factor in the specific action of anxiolytics.

Аналитическая модель малых колебаний сжимаемой магмы с реологией Максвелла в питающей системе вулкана. Часть 1. Осцилляции плотности

The analytical mathematical model is presented that describes one of the possible mechanisms for the occurrence of long-period seismic events that are often recorded near active volcanic centers. The feeding system of the volcano is modeled in the simplest form of a cylindrical channel filled with a compressible magmatic melt with the rheology of a Maxwell body. It is shown that such a magmatic body can experience harmonic damped oscillations, the damping coefficient of which is determined by the relaxation time of the magmatic melt. These fluctuations may appear as a response to a density perturbation caused by the influx of denser magma from deep layers or a change in pressure in the supply system of the volcano. The dependence of the natural oscillatory frequency on the physical characteristics of the magmatic melt and the geometric dimensions of the feed channel is shown. When the compressibility of the magmatic melt is taken into account, density perturbations depend on the size of the feeding system and are characterized by periodic oscillations, which are most pronounced near the channel axis. Oscillations are also experienced by the flow velocity component directed along the radius of the cylinder. The source mechanism of the long-period seismic events is discussed. The model is used to describe long-period oscillations recorded near Santiaguito (Guatemala).

The numerical prediction of the Earth’s polar motion based on an advanced multivariate algorithm

Since there are complicated changes in the polar motion (PM) from sub-annual to decadal, precisely predicting it is challenging. Here, we provide an advanced multivariate algorithm by combining an iterative oblique singular spectrum analysis (IOSSA) with pseudo data (IOSSApd) and consider more periodic and quasi-periodic signals, especially long-period oscillations (Ding et al., Geophys. Res. Lett., 2019, 46, 13765–13774) and multi-frequency Chandler wobble (Pan, International Journal of Geosciences, 2012, 3, 930–951), than previous studies. The IOSSA in oblique coordinates, due to its weak separability conditions, has a better separation performance than general singular spectrum analysis (SSA), and the IOSSApd approach further solved the shift problem. Upon using the IOSSApd method, the PM data can be separated into deterministic and stochastic components, extrapolated by the multiple-harmonic (MH) and autoregressive integrated moving average (ARIMA) models, respectively. Based on the IERS EOPC04 PM series, we produced multiple sets of PM predictions with a 1-year leading time and reported the IERS Bulletin A predictions as a comparison. For 90-day leading time predictions, the mean absolute errors (MAEs) of the x- and y-components were 7.69 and 5.12 mas, respectively, while the corresponding MAEs obtained by IERS Bulletin A were 9.45 and 5.69 mas, respectively. For up to 360 days, our algorithm obtains the MAEs of PM slowly accumulating to 12.98 mas on average, far better than the 19.14 mas for Bulletin A’s predictions (also significantly superior to the corresponding results given by previous studies). The prediction performance in the middle- and long-term prediction is further compared against the general SSA predictor. By virtue of weak periodic error, our results show that combining the IOSSApd + MH + ARIMA models improved the prediction success rate up to 75.39% and 69.58% for the x- and y-component, respectively.

Very-long-period oscillations in the atmosphere (0–110 km) – Part 2: Latitude– longitude comparisons and trends

Abstract. Measurements of atmospheric temperatures show a variety of long-term oscillations. These can be simulated by computer models and exhibit multi-annual, decadal, and even centennial periods. They extend from the ground up to the lower thermosphere. Recent analyses have shown that they exist in the models even if the model boundaries are kept constant with respect to influences of the sun, ocean, and greenhouse gases. Therefore, these parameters appear not to be responsible for the excitation of these oscillations, i.e. the oscillations might be rather self-excited. However, influences of land surface and vegetation changes had not been entirely excluded. This is studied in the present analysis. It turns out that such influences might be active in the lowermost atmospheric levels. Long-term trends of atmospheric parameters such as the temperature are important for the understanding of the ongoing climate change. Their study is mostly based on data sets that are 1 to a few decades long. The trend values are generally small and so are the amplitudes of the long-period oscillations. It can therefore be difficult to disentangle these structures, especially if the interval of trend analysis is comparable to the period of the oscillations. If the oscillations are self-excited, there may be a non-anthropogenic contribution to the climate change which is difficult to determine. Long-term changes of the cold-point tropopause are analysed here as an example.

Slow mode oscillations in curved arcade loops

ABSTRACT In this work we theoretically investigate the effect of curvature on the slow-mode oscillations in coronal loop arcade. A simple model of an arc circle magnetic slab is used to simulate curved coronal magnetic structures. Solving the set of magnetohydrodynamic (MHD) equations for a compressible plasma, we obtain the dispersion relation that governs the compressible MHD modes in the model. A band of slow body modes with phase speeds close to the internal tube speed and a single hybrid slow mode with phase speed close to the external tube speed are found to exist under typical coronal circumstances. The principal slow body and hybrid modes both produce radial kink-like displacements of the slab axis and distort its cross-section. These motions are accompanied with the dominating longitudinal oscillations. Such mode properties may result in Doppler shift and intensity oscillations as well as oscillating spatial displacements, observed in coronal loops. A number of observations of long-period oscillations in arcade loops are interpreted on the basis of the developed theory.

Rheology and breakdown energy of a shear zone undergoing flash heating in earthquake-like discrete element models

SUMMARYWe study the initiation and growth of a dry granular shear zone subjected to seismic shearing and flash heating from the perspective of a discrete element method. For this purpose, we created a semi-periodic numerical shear test similar to a rotary shear machine in which a 2 mm ×1.5 mm sample composed of micrometric cohesive disks is sheared in between two rigid walls. The strength of cohesive bonds is defined according to an elasto-brittle contact law calibrated to simulate peak and residual strength envelopes derived from rock mechanics tests. The sample is traversed by a pre-existing fracture and subjected to a vertical confining pressure (e.g. 112.5 MPa) and a velocity step function (e.g. 1 m s–1) applied on the top and bottom walls, respectively. Slip along the fracture induces the growth of a shear zone, which thickens by progressive abrasion of damaged material from cohesive blocks. We carried out two parametric studies to determine the rheology and physical properties of the shear zone for slip velocities and confining pressures characteristic of shallow earthquakes and several flash-heating temperatures. According to parametric studies, the mechanical behavior of the shear zone exhibits three distinct phases. The initial phase of rupture initiation is characterized by the propagation of a shear instability generated by the velocity step (phase 1). During this phase, friction and dilatancy curves are approximated by asymmetric peak functions whose amplitude and geometry are controlled primarily by confining pressure. In the intermediate phase of shear-zone growth, the sample displays an initial transient stage that asymptotically approaches steady state at submelting temperatures (phase 2). According to the inertial number, seismic shearing occurs under quasi-static conditions despite high shear rates. Thus, friction and dilatancy observed in all simulations are roughly constant regardless of slip velocity, confining pressure, and gouge zone thickness. In the final phase of shear weakening, the model evolves toward a new steady state at flash-heating temperatures (phase 3). Average friction and dilatancy are represented by sigmoidal decreasing curves that approach steady-state values lower than for phase 2. Predictably, the thermally weakened friction in steady state (μss ∼ 0.1) is close to the strength of frictionless granular samples sheared in quasi-static conditions. We calculate breakdown energies for the gouge and damage zones and the fracture energy at intermediate and high confining pressures. We show that breakdown energy fundamentally differs from fracture energy commonly used in seismology. The breakdown energy of the damage zones shows long-period damped oscillations weakly correlated with shear-stress fluctuations around average decaying values. Our results suggest that dilatancy is the primary energy sink within the damage zones at steady-state values. The breakdown energy components of the gouge zone follow a similar decaying trend as the average fracture energy but over a longer critical distance. Decohesion and dilatancy are the major energy sinks linked to gouge formation at intermediate pressures. In contrast, dilatancy and debonding frictional energies predominate at high confining pressures. Breakdown energy is equivalent to a fraction of fracture energy that nearly triples when doubling the confining pressure.

Comparative Dynamics Analysis of Simple Mathematical Models of the Plankton Communities Considering Various Types of Response Function

The paper proposes a two-component discrete-time model of the plankton community, taking into account features of the development and interaction of phytoplankton and zooplankton. To describe the interaction between these species and to compare the system dynamics, we use the following set of response functions: type II and III Holling function and the Arditi–Ginzburg response function, each of which describes trophic interactions between phytoplankton and zooplankton. An analytical and numerical study of the model proposed is made. The analysis shows that the variation of trophic functions does not change the dynamic behavior of the model fundamentally. The stability loss of nontrivial fixed point corresponding to the coexistence of phytoplankton and zooplankton can occur through a cascade of period-doubling bifurcations and according to the Neimark–Saker scenario, which allows us to observe the appearance of long-period oscillations representing the alternation of peaks and reduction in the number of species as a result of the predator-prey interaction. As well, the model has multistability areas, where a variation in initial conditions with the unchanged values of all model parameters can result in a shift of the current dynamic mode. Each of the models is shown to demonstrate conditional coexistence when a variation of the current community structure can lead to the extinction of the entire community or its part. Considering the characteristics of the species composition, the model with the type II Holling function seems a more suitable for describing the dynamics of the plankton community. Such a system is consistent with the idea that phytoplankton is a fast variable and predator dynamics is slow; thus, long-period fluctuations occur at high phytoplankton growth rates and low zooplankton ones. The model with the Arditi–Ginzburg functional response demonstrates quasi-periodic fluctuations in a narrow parametric aria with a high predator growth rate and low prey growth rate. The quasi-periodic dynamics regions in the model with the Holling type III functional response correspond to the conception of fast and slow variables, however in this case, the stability of the system increases, and the Neimark-Sacker bifurcation occurs even at a higher growth rate of zooplankton.

Multi-decadal oscillations of surface temperatures and the impact on temperature increases

The last IPCC assessment report indicated that natural climate variability could temporarily amplify or obscure anthropogenic climate change on decadal time scales. Here we analyse global mean surface temperatures in terms of such long-period variations. We find two main oscillations, a strong oscillation with a period of about 70 years and an amplitude of about 0.09 K and a quasi-bidecadal oscillation with an amplitude of about 0.06 K. The strong oscillation shows large hemispheric differences. In the Northern hemisphere the period is longer and the amplitude is larger (about 82 years and 0.18 K) compared to the Southern hemisphere (about 47 years and 0.065 K). No obvious hemispheric differences are observed for the quasi-bidecadal oscillation. Such long-period oscillations can strengthen or weaken the temperature increase if the oscillation positively or negatively adds to the underlying long-term trend.

Paleogene buried landscapes and climatic aberrations triggered by mantle plume activity

The Icelandic plume, a major mantle upwelling located beneath the North Atlantic Ocean, plays a dominant role in controlling periodic uplift of continental margins and of oceanographic gateways during Cenozoic times. Independent evidence shows that plume activity fluctuates on timescales of ≤1 Myr. Here, we describe and analyze a spectacular sequence of Paleogene buried landscapes imaged on seismic reflection surveys from the continental margin of northwest Europe. These transient landscapes recur on intervals of 2–3 Myrs, coincide with volcanic activity, and exhibit topographic relief of hundreds of meters. They probably represent the surficial expression of thermal fluctuations that spread radially away from the plume conduit. Five landscapes are coeval with global hyperthermal aberrations characterized by negative excursions of δ13C and by positive excursions of Fe intensity, which is a proxy for carbonate dissolution. We propose a causal relationship whereby thermal fluctuations of the mantle plume generate transient uplift and volcanic activity, which act to release significant quantities of greenhouse gases and thus trigger hyperthermal aberrations. A longer period oscillation of δ13C values is superimposed upon these aberrations that is attributable to a combination of silicate weathering and volcanic degassing caused by the interaction of plume activity and plate spreading.

On the exo-planet precession under torqes due to three celestial bodies with the evolution of the satellite's orbit

We investigate the non-resonant evolution of the axial tilt of hypothetical exo-Earth in the gravitational field of a star, planet's satellite (exo-Moon) and outer planet (exo-Jupiter). The exo-Earth is assumed to be rigid, axially symmetric ($A=B$) and almost spherical. We assume the orbits of the both exo-planets to be Keplerian ellipses with focus in the star, the orbit of exo-Moon to be an evolving Keplerian ellipse with slowly changing of ascending node longitude and periapsis argument. Assuming the frequencies of the unperturbed orbital elliptical motion to be of the order of unity, we obtain the canonical averaged equations describing the perturbed oscillations of the exo-Moon spin axis. These equations contain parameters changing slowly over time. Using the smallness of the planets' masses relative to the mass of the star, we have obtained simplified equations of oscillations of the exo-Earth spin axis by the small parameter method. Time integration of simplified equations gives the axial tilt of exo-Moon as a function of time. It is shown that the torques from the exo-Jupiter create a secular, long-period oscillation mode in axial tilt with a frequency equals to frequency of unperturbed spin axis precession of the exo-Earth. The impact of the exo-Moon on the evolution of the exo-Earth spin axis is that short-period harmonics appear in the oscillations of the axial tilt. The frequency of such oscillations is close to the precession frequency of the ascending node longitude of the exo-Moon orbit. We have calculated the evolution of exo-Earth axial tilt for two exo-planetary systems, i.e., for a system similar to the solar system, and for a planetary exo-system 7 Canis Majoris. The effect of destabilization (stabilization) of the exo-Earth tilt oscillations due to the torques exerted by exo-Moon and exo-Jupiter is described.

Oscillation suppression in a particle robotic arm by stiffness and damping regulation

Flexible arms have been widely studied by researchers in recent years, because of their adaptability and interactive security. Due to the low stiffness of the flexible arms, there will be large position deviation and long-period oscillation during de-actuated or excited, which is undesirable in many applications. This paper introduces the design principle and manufacturing method of a flexible arm with variable stiffness and damping to suppress oscillations. The arm is composed of three thin McKibben pneumatic artificial muscles and a chamber filled with discrete particles. The end position is determined by the air pressure input to the artificial muscles, the stiffness and damping of the arm can be further controlled by the vacuum pressure in the particle chamber. Models for stiffness, damping, and the effects on the oscillation suppression of the arm are established, and their validity is verified experimentally. Moreover, the significance of oscillation suppression in the proposed arm is proved by an image stabilization system.