Search

A series of sensitivity experiments on the Late Ordovician Earth's climate under different orbital configurations were conducted using the atmosphere-ocean general circulation model CESM1.2.2. It was found that the local annual mean surface temperature could vary by more than 5.5°C and the seasonal temperature by more than 23°C due to changes in orbital parameters. The global mean temperature was affected by less than 0.2°C due to precession, and an increase of about 1°C in the global mean temperature could be caused by a change in obliquity from 22.5° to 24.5°, due to the annual mean solar radiation received at high latitudes, together with the ice-albedo feedback. The global mean precipitation rate was found not to be impacted by orbital changes, but its spatial and temporal distribution was highly impacted; the north-south shift of the intertropical convergence zone was controlled by the precession, and an increase in precipitation at the poles was caused by increases in the obliquity. A great impact on the spatial pattern of summer monsoonal regions was also caused by orbital changes. A change in the global monsoon area by more than 40% could be caused by changes in precession; a mild effect on the mid-latitude and high-latitude monsoon area of approximately 10% was caused by obliquity. Although Late Ordovician was overall warm with its global mean surface temperature exceeding 18°C, deep snow can be accumulated over large areas of continents in the southern hemisphere under most orbital configurations, indicating the possibility of the formation of large ice sheets. [ABSTRACT FROM AUTHOR]

For much of the pelagic sedimentary record, time control is limited to the resolution of precession cycles (ca 20 kyr): the Milankovitch parameter that forms the most detailed metronome for the Cenozoic and Mesozoic Eras. The influence of precession is often detected in lithological alternations, where the duration represented by individual lithologies is not well constrained. Here the novel technique of extraterrestrial helium abundance (3HeET) is used to investigate the sedimentation dynamics and palaeoceanography within individual precessional cycles. High‐resolution 3HeET timescales were produced for four precession cycles from the rhythmically bedded Scaglia Bianca Formation, a sequence of Upper Cretaceous (Cenomanian) deep‐marine pelagic limestones from central Italy that are well characterized by cyclostratigraphy. Using 3HeET concentrations as a proxy for sedimentation rate allows instantaneous sedimentation rates and organic‐carbon mass accumulation rates to be calculated for each bed within a precession cycle. Eccentricity is known to modulate the amplitude of precession forcing, and precession cycles deposited under eccentricity maxima and minima were selected for comparison. Lithological changes through these chert–(black shale)–limestone cycles are explained using the concept of 'palaeoenvironmental thresholds'; these timescale calculations indicate that when the amplitude of precessional insolation forcing was greatest (at eccentricity maxima) the palaeoenvironmental system spent longer in the more nutrient‐rich environment under which siliceous and organic‐rich sediments were deposited, reflecting increased time spent above a 'threshold' insolation level. Estimates of primary productivity are relatively elevated for organic‐rich beds. An increase in the flux of terrestrial helium (4Heterr) during the deposition of cherts may have been coincident with an increase in terrestrially derived nutrients. The presented results indicate great potential for the use of 3HeET to understand past oceanographic, climatic and sedimentological processes at high temporal resolution. [ABSTRACT FROM AUTHOR]

In this section of Resonance, we invite readers to pose questions likely to be raised in a classroom situation. We may suggest strategies for dealing with them, or invite responses, or both. "Classroom" is equally a forum for raising broader issues and sharing personal experiences and viewpoints on matters related to teaching and learning science. [ABSTRACT FROM AUTHOR]

Libration and precession are different body forces that are ubiquitous in many rapidly rotating systems, particularly in geophysical and astrophysical flows. Libration is a modulation of the background rotation magnitude, whereas precession is a modulation of the background rotation direction. Assessing the consequences of these body forces in large-scale flows is challenging. The Ekman number, the ratio of the rotation time scale to the viscous time scale quantifying the rotation speed, is extremely small, leading to extremely thin and intense shear layers in the flows even when the amplitudes of the body forces are very small. We consider the consequences of libration and precession numerically in a geometrically simple container, a cube, which lends itself to very efficient, accurate, and robust numerical treatment, with the axis of rotation passing through opposite vertices, so that all walls of the cube are at oblique angles to the rotation axis. This results in the geometric focusing of inertial wavebeams reflecting off the walls, whereby the energy density of the wavebeams increases along with the magnitude of their wavevector. The nature of this focusing depends on the forcing frequency but not on the body force. In the inviscid setting, wavebeams form infinitesimally thin vortex sheets, and their energy density becomes unbounded upon focusing. We present linear inviscid ray tracing to set the scene for the focusing of wavebeams and then consider viscous problems at an Ekman number that is typical of current state-of-the-art laboratory experiments. We begin by considering the linear responses, which are comprised of focusing viscous shear layers, of which their details are mostly captured via ray tracing, and particular solutions accounting for the body forces. These have complicated spatio-temporal structures, which differ for libration and precession. Increasing the forcing amplitude from zero introduces nonlinear interactions, enhances the focusing effects via vortex tilting and stretching when the shear layers reflect at the walls, and also introduces temporal superharmonics and a mean flow. When the magnitude of the mean flow is within a few percent of the magnitude of the instantaneous flow, instabilities breaking the spatio-temporal symmetries set in. These are localized in the oscillatory boundary layers where the reflections are concentrated and introduce broadband dynamics in the boundary layers, with additional inertial wavebeams emitted into the interior. The details again depend on the specifics of the body forces. [ABSTRACT FROM AUTHOR]

Late Pleistocene glacial terminations are caused by rising atmospheric CO2 occurring in response to atmospheric and ocean circulation changes induced by increased discharge from Northern Hemisphere ice sheets. While climate records place glacial terminations coincident with decreasing orbital precession, it remains unclear why a specific precession minimum causes a termination. We compare the orbital and ice volume configuration at each precession minima over the last million years to demonstrate that eccentricity, through its control on precession amplitude, period and coherence with obliquity, along with ice sheet size, determine whether a given precession minimum will cause a termination. We also demonstrate how eccentricity controls obliquity maxima and precession minima coherence, varying the duration of glaciations. Glaciations lasting ∼100 thousand years are controlled by Earth's eccentricity cycle of the same period, while the shortest (20–40 ka) and longest (155 ka) occupy the maxima and minimums of the 400 thousand year eccentricity cycle. Plain Language Summary: The Milankovitch theory of the ice ages predicts that the growth and collapse of Pleistocene ice sheets is paced by the cycles in high latitude solar insolation that accompany variations in Earth's orbital motion. The orbital modes that dominate frequencies of incoming solar radiation are obliquity and precession, which operate at periodicities of approximately 40 and 20 thousand years, respectively. The dominant frequency at which ice sheets grow and collapse over the last million years is, however, approximately 100 thousand years, a closer match to eccentricity, an orbital period near absent from past solar radiation. Through a comparison between Earth's orbital configuration and an approximation of past global ice volume, we identify that the precession minima that trigger ice sheet collapse occur at distinct configuration of eccentricity and ice sheet size. In most cases terminations occur when precession minima align with obliquity maxima. We find that this coherence is influenced by the duration of precession cycles, which is in turn controlled by eccentricity. From these observations, we conclude that orbital eccentricity, through its control on both the amplitude and period of precession, paces the timing of glacial terminations and the size of Late Pleistocene ice sheets. Key Points: Late Pleistocene glacial terminations occur at distinct configurations of orbital precession, obliquity, eccentricity and ice volumeEccentricity controls the duration of precession cycles, and therefore the coherence of obliquity and precessionOrbital eccentricity, through its control on the amplitude and period of precession, paces Late Pleistocene glaciations [ABSTRACT FROM AUTHOR]

The influence of space curvature on input of magnetic field outside neutron star to moment of inertia tensor of radiopulsar in case of Shwartzshild metric is considered. It is considered both the case of pure dipolar magnetic field and the case of "small scale" magnetic field but only in the case of a single axisymmetric harmonic. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) serves not only as the "water tower" of Asia but also as an important source in the global atmospheric dust cycle. While our knowledge of modern dust activity and its impacts and interactions with climate change in the TP has greatly advanced in the past decades, the emission, transport, and deposition of dust on the geological time scale remains unclear. This study analyzed a 7.6‐m thick sedimentary sequence consisting of loess and sand from the Yarlung Tsangpo River (YTR) valley in the southern TP. The sequence chronology was established using nineteen K‐feldspar post‐infrared infrared stimulated luminescence (pIRIR) ages, which ranged from 47.11 ± 1.95 to 116.65 ± 5.55 ka in a general stratigraphical order. The dust sedimentation rate and sorting coefficient of grain size were used to reflect dust activity and near‐surface wind, respectively. The results indicated that dust activity in the southern TP is mainly regulated by the near‐surface wind intensity and follows the variation pattern of precession, although the waxing and waning of mountain glaciers also affect the amplitude of dust activity. This pattern is not consistent with the Greenland dust record, which follows the variation pattern of obliquity. Therefore, dust accumulation in the southern TP is concluded to be primarily controlled by the South Asian winter monsoon (SAWM) forced by precession, whereas dust accumulation in Greenland is closely related to the intensity of the high‐level westerlies forced by obliquity. Plain Language Summary: TP serves as an important source in the global atmospheric dust cycle, but the emission, transport, and deposition of dust in the geological time scale remain poorly understood. This study presents a Late Pleistocene record of dust activity based on a 7.6‐m thick sedimentary sequence from the YTR valley in southern TP. The results indicated that dust activity in southern TP is primarily regulated by the near‐surface wind intensity and follows the variation pattern of precession. When precession is large, the Northern Hemisphere's summer solstice is located at the aphelion, resulting in a lower Northern Hemisphere summer insolation (NHSI). Lower NHSI reduces winter temperature in the Northern Hemisphere, thereby increasing the temperature difference between the Indian Ocean and the TP. Consequently, wind over the YTR valley is strengthened, and the dust activity increases. Moreover, the variation amplitude of dust activity was revealed to be also affected by the waxing and waning of mountain glaciers. Dust accumulation was found to be asynchronous between the southern TP and Greenland. This asynchronous phenomenon is assumed to be related to the differential response of orbital parameters between the high‐level westerlies and near‐surface wind in southern TP. Key Points: Closely spaced luminescence dating for Late Pleistocene loess in the southern Tibetan Plateau is presentedDust activity follows the variation pattern of precession, despite mountain glaciers also affecting dust activity amplitudeAsynchronous variations of dust accumulation in the southern Tibetan Plateau and Greenland during the Late Pleistocene [ABSTRACT FROM AUTHOR]

A modification to the vis-viva equation that accounts for general relativistic effects is introduced to enhance the accuracy of predictions of orbital motion and precession. The updated equation reduces to the traditional vis-viva equation under Newtonian conditions and is a more accurate tool for astrodynamics than the traditional equation. Preliminary simulation results demonstrate the application potential of the modified vis-viva equation for more complex n-body systems. Spherical symmetry is assumed in this approach; however, this limitation could be removed in future research. This study is a pivotal step toward bridging classical and relativistic mechanics and thus makes an important contribution to the field of celestial dynamics. [ABSTRACT FROM AUTHOR]

Until now, the comprehensive structural analysis of single crystals of zeolite ECR-1, an aluminosilicate with the EON topology, has been hindered owing to the submicron dimensions of the obtained crystals. Additionally, this zeolite, which is characterized by a topology comprising alternating periodic building units of MAZ and MOR layers, exhibits stacking faults that impede accurate refinement through the Rietveld method. In this report, we present, for the first time, the structure of ECR-1 elucidated by studying a nanocrystal with a significantly reduced number of stacking faults. The sample used was synthesized hydrothermally using trioxane as the organic structure-directing agent. The structure determination was conducted using precession electron diffraction (PED) at 103 K. Partial dehydration occurred owing to the high vacuum conditions in the TEM sample chamber. From the dynamical refinement (Robs = 0.097), 8.16 Na+ compensating cations were localized on six distinct crystallographic sites, along with approximately four water molecules per unit cell. Furthermore, a canonical Monte Carlo computational study was conducted to compare the experimental cationic distribution and location of water molecules with the simulation. [ABSTRACT FROM AUTHOR]

The effects of obliquity and precession on conditions favorable for Northern Hemisphere glaciation are explored using an energy balance and mass balance model of equilibrium line altitude (ELA), the height on a glacier where accumulation and ablation are in balance annually. Climate forcing for the ELA model is obtained from idealized single‐forcing orbital simulations with two atm‐ocean general circulation models, Geophysical Fluid Dynamics Laboratory (GFDL) CM2.1 and National Center for Atmospheric Research (NCAR) Community Earth System Model version 1.2. Over Scandinavia and Baffin Island, the respective locations in which the Scandinavian and Laurentide ice sheets are thought to have originated, low obliquity and perihelion at the boreal winter solstice are associated with lower ELA values, as would be expected from the orbital theory of the ice ages. Linear reconstructions of ELA variations over the past 800 kyr indicate that precession dominated ELA variations in Scandinavia and Baffin Island in the GFDL model, and in Scandinavia in the NCAR model. Obliquity and precession played equal roles in Baffin Island in the NCAR model. A decomposition of the ELA responses finds that the effects of ablation on ELA are much larger than the effects of precipitation. Overall, the findings of this study point to precession being a more important factor in glacial inception than obliquity, which contrasts with previous findings in which obliquity had a slightly larger effect on positive degree days (PDDs), a simple metric for ablation. This is likely due to differences in seasonality of melt from the ELA model and PDDs. Plain Language Summary: Large ice sheets alternately grew and decayed over Eurasia and North America during the past several million years. These cycles of glaciation are understood to be a response to changes in the shape of Earth's orbit, the timing of its closest passage to the Sun, and the tilt of its axis, which occur in predictable cycles. Using two global climate models and a model of how mass and energy are exchanged between a glacier and its environment, we found that the climate is more conducive to sea ice growth when the tilt of Earth's axis is smaller than today. The climate is also more conducive for growth when Earth is closest to the Sun in Northern Hemisphere winter rather than summer. Our results indicate that changes in orbital shape and timing of Earth's closest passage to the Sun exert a stronger effect than changes to the tilt of Earth's axis. We also found that changes in the processes that cause an ice sheet to lose mass (primarily melting) are more important than processes that cause it to gain mass (i.e., precipitation). Key Points: Glacier equilibrium line altitude (ELA) is more sensitive to precession than obliquity, unlike positive degree daysThe results were sensitive to how temperature was simulated in each climate modelAblation was more important than precipitation in determining ELA anomalies [ABSTRACT FROM AUTHOR]

The subject of the study is the problem of precession of a gyrostat with a fixed point in three homogeneous force fields. The class of precessional movements under consideration is characterized by the properties of constancy of the nutation angle and commensurability of the precession rates and the gyrostat's own rotation. The equations of motion of the gyrostat are reduced to three second-order differential equations with respect to the precession rates and the proper rotation of the gyrostat. Integration of these equations was carried out in the case of precessional-isoconic movements (the speeds of precession and proper rotation are equal) and in one case the resonant values of the speeds of precession and proper rotation (the precession speed is twice the speed of proper rotation – resonance 2 : 1). It is proven that the solutions obtained in the article are characterized by elementary functions of time. [ABSTRACT FROM AUTHOR]

In the realm of ballistic target analysis, micro-motion attributes, such as warhead precession, nutation, and decoy oscillations, play a pivotal role. This paper addresses these critical aspects by introducing an advanced analytical model for assessing the Doppler power spectra of convex quadric revolution bodies during precession. Our model is instrumental in calculating the Doppler shifts pertinent to both precession and swing cones. Additionally, it extends to delineate the Doppler power spectra for configurations involving cones and sphere–cone combinations. A key aspect of our study is the exploration of the effects exerted by geometric parameters and observation angles on the Doppler spectra, offering a comparative perspective of various micro-motion forms. The simulations distinctly demonstrate how different micro-motion patterns of a cone influence the Doppler power spectra and underscore the significance of geometric parameters and observational angles in shaping these spectra. This research not only contributes to enhancing LIDAR target identification methodologies but also lays a groundwork for future explorations into complex micro-motions like nutation. [ABSTRACT FROM AUTHOR]

Gyroscopes are devices used for orientation determination however mechanical gyroscopes are used for orientating and balancing via gyroscopic torque. This torque is generated by the precession speed given to the rotating objects from one of the axes other than the rotation axes. In this study, the gyroscopic torque was calculated using dynamic analysis onto a single flywheel mechanical gyroscope design created. Free vibration frequencies were determined by modal analysis. Dynamic responses for the movement of the gyroscope with a flywheel, which is mounted vertically and balances the weight torque, are investigated on the basis of classical (Newtonian) mechanics. When the flywheel rotates in the range of 0-250 rad/s, it does not correspond to any natural frequency. Torque of 0.468 Nm is offset by a precession velocity of 0.922 rad/s. Nutation oscillations disappears when torsional damping is given to the joint where the gyroscope is attached to the ground. The free vibration frequencies change in the damped state. [ABSTRACT FROM AUTHOR]

Due to the gyroscopic torque production ability, mechanical gyroscopes are frequently used for balancing fully suspended or single/two-wheeled land vehicles such as airplanes and spacecraft. They produce gyroscopic torque thanks to the flywheel rotating at high speed. Precession is required to control this torque. In the study, 415 precession data were collected by performing a rigid dynamic analysis of a mechanical gyroscope. A non-linear autoregressive artificial neural network (NAR) is used to estimate this velocity. In the model obtained, the correlation value was 0.998 and the root mean square of error (RMSE) value was 0.016 rad/s. A high linear relationship was detected between the model output and the data set. The NAR network has eliminated the need for any pre-processing on the data. The network parameters used and the estimation performances obtained with this model are presented in the study. [ABSTRACT FROM AUTHOR]

Core-mantle friction induced by the precession of the Moon's spin axis is a strong heat source in the deep lunar mantle during the early phase of a satellite's evolution, but its influence on the long-term thermal evolution still remains poorly explored. Using a one-dimensional thermal evolution model, we show that core-mantle friction can sustain global-scale partial melting in the upper lunar mantle until ∼3.1 Ga, thus accounting for the intense volcanic activity on the Moon before ∼3.0 Ga. Besides, core-mantle friction tends to suppress the secular cooling of the lunar core and is unlikely to be an energy source for the long-lived lunar core dynamo. Our model also favours the transition of the Cassini state before the end of the lunar magma ocean phase (∼4.2 Ga), which implies a decreasing lunar obliquity over time after the solidification of the lunar magma ocean. Such a trend of lunar obliquity evolution may allow volcanically released water to be buried in the lunar regolith of the polar regions. As a consequence, local water ice could be more abundant than previously thought when considering only its accumulation caused by solar wind and comet spreading. [ABSTRACT FROM AUTHOR]

The aim of the current paper is to apply Bambi's method (Bambi, 2015) to a source which contains two or more simultaneous triads of variability components. The joint x variable that can be composed in this case, unlike some previous studies, allows the goodness of the fit to be tested. It appears that a good fit requires one of the observation groups to be disregarded. Even then, the model's prediction for the mass of the neutron star in the accreting millisecond pulsar IGR J17511-3057 is way too high to be accepted. [ABSTRACT FROM AUTHOR]

Chisel marks on a stone uncovered in Rupinpiccolo protohistoric hill fort from north‐eastern Italy were suggested to be a representation of the night sky (Bernardini et al. 2022 Documenta Praehistorica XLIX). The patterns of the 29 marks are analyzed here to establish if they reproduce popular stellar asterisms. Nine marks are found to match the Tail of Scorpius and five the Orion's Belt, together with Rigel and Betelgeuse. Nine marks are found in the approximate position of the Pleiades showing some match with the cluster members. On the back side, 5 marks possibly reproduce Cassiopeia. One mark slightly North of Orion cannot be identified. The 28 marks show a Pearson correlation coefficient r$$ r $$(28) with stellar positions higher than 0.99 with a probability p$$ p $$ of a wrong correlation lower than 0.001. Departures are about one degree, or about 7 mm, as the mean diameter of the marks, which suggests a manufacturing limitation in the charting. The fort dates ≈$$ \approx $$1800–400 BCE when Scorpius and Orion showed about the same orientation at the heliacal rising. The unidentified mark challenges the whole picture. We suggest it could have been the progenitor of a failed supernova, thus offering also the possibility of a verification. [ABSTRACT FROM AUTHOR]

The latest results of the most detailed analysis of multi-epoch polarization-sensitive observations of active galactic nuclei (AGN) jets at parsecs scales by very long baseline interferometry (VLBI) reveal several characteristic patterns of linear polarization distribution and its variability [1, 2]. Some of the observed profiles can be reproduced by a simple model of a jet threaded by a helical magnetic field. However, none of the models presented to date can explain the observed polarization profiles with an increase in its degree towards the edges of the jet, and accompanied by a "fountain" type electrical vector pattern and its high temporal variability in the center. Based on simulations of the VLBI observations of relativistic jets, we show here that the observed transverse linear polarization profiles can be naturally produced in a model of jets precessing on ten-years scales. In this scenario, due to the finite resolution of VLBI arrays, the initially strong polarization along the jet axis is blurred due to the superposition of regions whose polarization angle changes significantly when projected onto the sky plane. In our simulations, we qualitatively reproduce the distribution of the electric vector and its variability, though the polarization distribution images are characterized by a bright spine due to weak suppression of polarized emission, which is poorly consistent with observations of quasars. More effective depolarization can be obtained in models with the suppressed emission of the jet spine. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Signal Processing is the property of Journal of Signal Processing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Orbital precession has been linked to glacial cycles and the atmospheric carbon dioxide (CO2) concentration, yet the direct impact of precession on the carbon cycle is not well understood. We analyze output from an Earth system model configured under different orbital parameters to isolate the impact of precession on air‐sea CO2 flux in the Southern Ocean—a component of the global carbon cycle that is thought to play a key role on past atmospheric CO2 variations. Here, we demonstrate that periods of high precession are coincident with anomalous CO2 outgassing from the Southern Ocean. Under high precession, we find a poleward shift in the southern westerly winds, enhanced Southern Ocean meridional overturning, and an increase in the surface ocean partial pressure of CO2 along the core of the Antarctic Circumpolar Current. These results suggest that orbital precession may have played an important role in driving changes in atmospheric CO2. Plain Language Summary: Over the past one million years, Earth has experienced several glacial and interglacial periods. As a glacial period is ending, carbon in the atmosphere can rise by up to 50%. The cause for this change is currently unknown, but most theories suggest that this carbon is released from the deep ocean into the atmosphere. The Southern Ocean surrounding Antarctica is the location of a lot of carbon outgassing from the deep ocean into the atmosphere, so it could be responsible for some of this change in atmospheric carbon. One of Earth's orbital cycles, precession, has been shown to change circulation in the Southern Ocean, that can affect how much carbon is carried from the deep ocean to the surface and released into the atmosphere. This paper uses simulations of a climate model to show that high precession corresponds to a 20% increase in the release of carbon from the Southern Ocean into the atmosphere. These findings suggest that precession could have affected changes in past atmospheric carbon concentrations. Key Points: Increased insolation during austral summer due to orbital precession shifts the southern westerlies polewardPoleward shifted westerlies enhance CO2 outgassing due to increased turbulent exchange and vertical transport of carbon‐rich watersEnhanced transport of carbon‐rich waters is driven by a deepening of the overturning circulation in response to poleward shifted winds [ABSTRACT FROM AUTHOR]

The design of the electric machine with three degrees of freedom of the rotor with an external magnetic core, containing permanent magnets, and an internal magnetic core is considered. The both magnetic cores are rotating. The stator windings (control winding and two-phase rotation winding) are located in the air gap between the magnetic cores. The windings are powered by alternating current of corresponding phase. The positive property of rotor gyrostabilization in such structure is shown. At the same time, the negative fact consists in the nutation under the conditions of forced change in the orientation of rotation axis. There are no magnetic losses in the structure due to synchronous rotation of both external and internal magnetic cores. The immobility of the center of mass is assumed. There are no losses that give a non-conservative mechanical system. The mathematical model of the mechanic system and magnetic field is developed to compute the electromagnetic torques acting on the rotor. The expressions for electromagnetic torque components are obtained to use them in the Comsol Multiphysics interface. The effect of the sinusoidal and pulse currents in the control winding on the nutation swing is studied. The optimality of the control winding supplied by undisturbed sinusoidal current or the pulse current having square-wave length of about one-third of the period is revealed. References 15, figures 6, table 1. [ABSTRACT FROM AUTHOR]

Libration and precession are different body forces that are ubiquitous in many rapidly rotating systems, particularly in geophysical and astrophysical flows. Libration is a modulation of the background rotation magnitude, whereas precession is a modulation of the background rotation direction. Assessing the consequences of these body forces in large-scale flows is challenging. The Ekman number, the ratio of the rotation time scale to the viscous time scale quantifying the rotation speed, is extremely small, leading to extremely thin and intense shear layers in the flows even when the amplitudes of the body forces are very small. We consider the consequences of libration and precession numerically in a geometrically simple container, a cube, which lends itself to very efficient, accurate, and robust numerical treatment, with the axis of rotation passing through opposite vertices, so that all walls of the cube are at oblique angles to the rotation axis. This results in the geometric focusing of inertial wavebeams reflecting off the walls, whereby the energy density of the wavebeams increases along with the magnitude of their wavevector. The nature of this focusing depends on the forcing frequency but not on the body force. In the inviscid setting, wavebeams form infinitesimally thin vortex sheets, and their energy density becomes unbounded upon focusing. We present linear inviscid ray tracing to set the scene for the focusing of wavebeams and then consider viscous problems at an Ekman number that is typical of current state-of-the-art laboratory experiments. We begin by considering the linear responses, which are comprised of focusing viscous shear layers, of which their details are mostly captured via ray tracing, and particular solutions accounting for the body forces. These have complicated spatio-temporal structures, which differ for libration and precession. Increasing the forcing amplitude from zero introduces nonlinear interactions, enhances the focusing effects via vortex tilting and stretching when the shear layers reflect at the walls, and also introduces temporal superharmonics and a mean flow. When the magnitude of the mean flow is within a few percent of the magnitude of the instantaneous flow, instabilities breaking the spatio-temporal symmetries set in. These are localized in the oscillatory boundary layers where the reflections are concentrated and introduce broadband dynamics in the boundary layers, with additional inertial wavebeams emitted into the interior. The details again depend on the specifics of the body forces.

We consider the influence of space curvature in the Schwarzschild metric on the contribution of the magnetic field outside the neutron star to the moment of inertia of a radio pulsar. Our consideration is restricted only to the simplest configuration of the magnetic field, when it can be described by only one harmonic. We show that at a fixed magnetic field strength on the stellar surface the influence of space curvature reduces the contribution of the magnetic field outside the star to the departure of the inertia tensor from the spherical one several-fold. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Two structures of electric machines with three degrees of freedom of the rotational movement of the rotor are considered - with an external and an internal rotor held on an internal cardan suspension. A three-plane symmetric magnetic system was chosen for the comparative analysis and such a choice was justified. Limitations are formulated that allow considering the rotor as a conservative mechanical system, as well as considering the magnetic field in the electric machine as magnetostatic. Mathematical models of the rotational motion of a body with a fixed center of mass, as well as the force interaction of the magnetic field of a permanent magnet located on the rotor and the control winding located on the stator, are given. The peculiarities of the distribution of electromagnetic forces in both structures are analyzed and the greater efficiency of the formation of these forces in the structure with an internal rotor is shown. Expressions for the components of the electromagnetic moment for use in the "COMSOL Multiphysics" interface are obtained. Forced precession movement for both structures was analyzed in the case of equal radii of the control windings and in the case of the same dimensions of the magnetic systems. It was determined that the structure with an external magnetic circuit is able to provide an order of magnitude smaller angular velocity of precessional movement and, at the same time, an equally smaller range of nutation. [ABSTRACT FROM AUTHOR]

Numerous palaeoclimatic records have shown that precession plays a dominant role in the Asian monsoon precipitation. However, the impact and mechanism of precession change on the East Asian summer monsoon (EASM) under high CO 2 conditions have yet to be studied. The mid-Pliocene (∼3.3–3.0 Ma) was the most recent warm interval during which atmospheric CO 2 concentrations were similar to the present level of ∼400 ppmv. Therefore, it is often regarded as an analog for a near-future climate scenario. Here, the influence of precession change on EASM is investigated through numerical climate modeling using the mid-Pliocene as a test case. The results show that from the minimum to maximum of the precession, the summer temperature maximum zone shifted northward from ∼30°N to ∼45°N and the summer precipitation increased by ∼60% over the mainland East Asia. The simulations also show that the top-of-atmosphere insolation increased significantly in the Northern Hemisphere summer over mid- and high-latitudes and increased slightly over low latitudes from the precession minimum to maximum, leading to a substantial increase in the thermal contrast between the mainland East Asia and the equatorial western North Pacific. In this scenario, the western North Pacific subtropical high intensified and expanded, and the ITCZ migrated northward over South and Southeast Asia and was shifted southward over the area between the 110°E and 130°E, thereby leading to the rain belt penetration into northern China. [ABSTRACT FROM AUTHOR]

MS Vienna, Österreichische Nationalbibliothek, 5311, fol. 137r, contains an unusual record of astronomical observations, among which are measurements of solar and stellar altitudes carried out with large quadrants in Bologna, Montpellier, and Genoa between 1305 and 1312. An analysis of this observational data reveals a high level of precision and accuracy, as the astronomer responsible achieved a mean error of only 0;2° during an extended run of measurements of solar noon altitudes made between December 1305 and March 1306. Other passages on the same manuscript page mention Johannes de Luna, a German astrologer-astronomer active in Bologna between c. 1299 and 1312. References to his name in 14th-century manuscripts shed light on his involvement in contemporary attempts to correct the Toledan Tables and revise their model of precession on an observational basis. [ABSTRACT FROM AUTHOR]

Copyright of Jurnal Ilmiah Islam Futura is the property of Jurnal Ilmiah Islam Futura and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Technical Electrodynamics / Tekhnichna Elektrodynamika is the property of National Academy of Sciences of Ukraine, Institute of Electrodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The solar wind‐Jovian magnetosphere‐ionosphere interaction is studied from the global magnetohydrodynamic simulation. The calculation considers the high‐speed solar wind, Io plasma emission, high‐speed rotation, ionospheric ions, and precession of magnetic field, and consequently reproduces the confinement of Jovian magnetic field, distributions of O+ and H+, supply of H+ by the polar wind, the interchange instability, and the current system that maintains co‐rotation. The radial transport process of plasma generated from Io is traceable from this solution, such that the transport mechanism gradually changes from the Io torus to the distant tail. In the transport of Io plasma, the precession plus interchange instability is effective near 10–15 Rj, interchange instability is predominant around 15–20 Rj, and the centrifugal force is predominant beyond 25 Rj. The current system supplies torque from the planet to co‐rotating plasma beyond 25 Rj to compensate the rotation delay. The associated upward field‐aligned current (FAC) is connected to the main emission (ME) in the ionosphere. The polar emission (PE) position coincides with that of downward feedback current of upward FAC causing the ME. High‐speed polar wind develops in the ME and in the polar cap, while slow polar wind develops in lower latitudes. In the middle of transport, Io plasma is mixed around 15 Rj with H+ supplied from the ionosphere by the low‐speed polar wind. Afterward, mixed plasma diffuses outward. The equatorial diffuse emission occurs in the projected position of the plasma mixing process. Key Points: Around 10–15 Rj in the equatorial plane, precession effect overwhelms interchange for the outward transport of Io plasmaIo plasma is interchange unstable around 15–20 Rj and here diffuses outward while being mixed with H+ from the ionosphereThe equatorial diffuse emission is projected with the low‐speed polar wind to the outer shell of the Io torus around 15–20 Rj in the equatorial plane [ABSTRACT FROM AUTHOR]

The structure of an electric machine with a rotor, which has three degrees of freedom of rotation (EMTR) and consists of external and internal magnetic circuits, is considered. Between them, in the air gap of a spherical configuration, there is an m-phase rotation winding and a control winding. The excitation of the magnetic field in the EMTR is carried out by means of permanent magnets located on the external magnetic circuit. The scope of application of EMTP in systems of stabilization, observation, tracking, where the rotor performs the function of a gyro-stabilizing element, is outlined. Taking into account the structure of the considered EMTR, the absence of eddy currents in the design and the suitability of the mathematical model of the static magnetic field are substantiated. The calculation of the torque of the EMTR with two- and three-phase rotational windings at different angles of rotor’s inclination relative to the stator axis has been performed. It is shown that the rotation torque of the three-phase winding is 20% higher than that of the two-phase winding. A significant influence of the control winding on the torque of the three-phase winding and approximately the same influence of the two- and three-phase rotation windings on the processional torque with a significant value of the rotor inclination angle are noted. References 7, figures 8, tables 1. [ABSTRACT FROM AUTHOR]

Sidewall tapering is one of the main limitations in ultrashort pulse (USP) laser machining and is associated with the beam shape and self-limiting effect. Laser processing with a precession beam is a potential solution to overcome this limitation. A study into the effects of precession parameters on the taper angle in microhole drilling of a nickel alloy is reported in this paper. The effects of three key precession parameters, i.e., incident angle, relative distance between the focuses of the precession and individual beams, and scanning speed, have been investigated in detail. Experiments were performed to drill through holes with aspect ratios up to 20:1 and diameters ranging from 100 to 500 μm over 0.6–2 mm thick nickel alloy substrates. Experiment results showed that all the considered parameters/factors were significant and affected the hole tapering in different ways. In addition, there were important interaction effects between two of the factors, i.e., incident angle and focus position, in some cases. The optimal parameters to minimize the tapering effect are suggested, and the mechanism is discussed in detail. The precession laser machining showed clear advantages in overcoming the limitations to associated with conventional USP laser machining. Fabricating microholes with high geometrical accuracy, i.e., with straight side walls and zero taper angles, is feasible with the use of a precession beam. The results clearly show the potential of precession laser processing and the capabilities that the technology can offer for a range of laser micromachining applications in different industries, such as microelectronics, automotive, and aerospace. [ABSTRACT FROM AUTHOR]

The dynamics of a rotor with a massive disk is considered for the case of interaction with oscillation limiters represented by viscoelastic supports discretely arranged in the disk rotation plane. Differential equations that describe the transverse radial and angular rotor oscillations in the course of rotation are obtained. The solution is presented in the form of a second-kind integral of the Fredholm equation. The supercritical rotor behavior after the Poincaré–Andronov–Hopf bifurcation caused by internal friction in the shaft material is studied. A generalized definition of the rotor precession index has been introduced, making it possible to calculate the frequency and direction of precession based on the information concerning transverse rotor oscillation. [ABSTRACT FROM AUTHOR]

The loess-paleosol sequences on the Chinese Loess Plateau (CLP) are among the best terrestrial archives for recording orbital-scale global paleoenvironmental and East Asian monsoon changes during the Quaternary Period. Dust provenance and climate patterns vary across the CLP due to its vast size. However, whether available climate proxies were influenced by varying signals from the different dust source areas remains unknown. Here we present time series analysis results of high-resolution grain-size records from four loess sections (Jingbian, Xifeng, Baoji, and Weinan sections) spanning a north to south transect in the eastern CLP across the past 0.7 Ma. By comparison with data from the previously reported Luochuan section in the eastern CLP, and the Gulang, Menyuan, Jingyuan, Lanzhou, and Linxia sections in the western CLP, it is revealed that the dominant orbital signal in grain size variations in the eastern CLP is the ∼100-kyr ice-age cycle, with precession only very weakly expressed. By contrast, western CLP records exhibit both ∼100-kyr and ∼ 20-kyr precession cycles. We show that this contrasting orbital patterns between the eastern and western CLP are likely to be influenced by the climate signals from the respective source regions. We propose that the grain size variations in the western CLP not only contain the ∼100-kyr ice-age related winter monsoon cycles but also precession cycles related to the mid-latitude Westerlies and the Tibetan Plateau. The grain size variations in the eastern CLP are, by contrast, mainly influenced by ∼100-kyr ice-age cycle-regulated winter monsoon changes. The spatial diversity of periodicity in loess grain-size records from the CLP suggests that caution should be taken when discussing the periodicities of loess records based on any single site. • Periodicities in loess grain-size vary across the CLP. • Climatic signals from the source areas can be inherited by loess grain size. • Significance of the loess grain size can be various in different regions. • East Asian winter monsoon lacked the ∼20-kyr period during the past 0.7 Ma. [ABSTRACT FROM AUTHOR]

The design of the electric machine with three degrees of freedom of the rotor with an external magnetic core, containing permanent magnets, and an internal magnetic core is considered. The both magnetic cores are rotating. The stator windings (control winding and two-phase rotation winding) are located in the air gap between the magnetic cores. The windings are powered by alternating current of corresponding phase. The positive property of rotor gyrostabilization in such structure is shown. At the same time, the negative fact consists in the nutation under the conditions of forced change in the orientation of rotation axis. There are no magnetic losses in the structure due to synchronous rotation of both external and internal magnetic cores. The immobility of the center of mass is assumed. There are no losses that give a non-conservative mechanical system. The mathematical model of the mechanic system and magnetic field is developed to compute the electromagnetic torques acting on the rotor. The expressions for electromagnetic torque components are obtained to use them in the Comsol Multiphysics interface. The effect of the sinusoidal and pulse currents in the control winding on the nutation swing is studied. The optimality of the control winding supplied by undisturbed sinusoidal current or the pulse current having square-wave length of about one-third of the period is revealed. References 15, figures 6, table 1. .