Ice giant seismology: prospecting for normal modes

2020 ◽  
Vol 378 (2187) ◽  
pp. 20190475 ◽  
Author(s):  
A. James Friedson
Keyword(s):  
Spatial Structure ◽  
Gravity Field ◽  
Normal Modes ◽  
Pressure Level ◽  
Temperature Variations ◽  
Technical Challenge ◽  
Velocity Amplitude ◽  
Periodic Pressure ◽  
Gravitational Influence ◽  
Orbiting Spacecraft

The properties of ice giant normal mode oscillations, including their periods, spatial structure, stratospheric amplitudes and relative influence on the external gravity field, are surveyed for the purpose of formulating the best strategy for their eventual detection. Measurement requirements for detecting a normal mode's periodic pressure and temperature variations, including a possible stratospheric signal, and its effect on the external gravity field, are discussed in terms of its radial velocity amplitude at the 1 bar pressure level. It is found that for reasonable amplitudes, detection of the pressure and temperature variations of ice giant normal modes presents an extraordinary technical challenge. The prospects for detecting their gravitational influence on an orbiting spacecraft are more promising, with requirements that lie within the range of current technology. This article is part of a discussion meeting issue ‘Future exploration of ice giant systems’.

Observations of the spatial structure of interstellar hydrogen

1967 ◽  
Vol 31 ◽  
pp. 45-46
Author(s):  
Carl Heiles
Keyword(s):  
High Resolution ◽  
Spatial Structure ◽  
Velocity Dispersion ◽  
Temperature Variations

High-resolution 21-cm line observations in a region aroundlII= 120°,b11= +15°, have revealed four types of structure in the interstellar hydrogen: a smooth background, large sheets of density 2 atoms cm-3, clouds occurring mostly in groups, and ‘Cloudlets’ of a few solar masses and a few parsecs in size; the velocity dispersion in the Cloudlets is only 1 km/sec. Strong temperature variations in the gas are in evidence.

scholarly journals Three years of high precision gravity measurements at the gravimetric station of Brasimone - Italy

1998 ◽  
Vol 41 (2) ◽  
Author(s):  
G. Casula
Keyword(s):  
Gravity Field ◽  
High Precision ◽  
Nuclear Power ◽  
Meteorological Data ◽  
Normal Modes ◽  
Superconducting Gravimeter ◽  
Mass System ◽  
Global Geodynamics ◽  
Local Gravity ◽  
Italian Apennines

From August 1995 up to now, at the Enea Research Center of Brasimone, in the Italian Apennines between Bologna and Florence (Italy: 44º07'N, 11º.07'E, 890 m height), the superconducting gravimeter GWR model TT70 number T015 has been continuously recording the variation of the local gravity field, in the frame of the Global Geodynamics Project. The gravimetric laboratory, being a room of the disused nuclear power plant of Brasimone, is a very stable site, free from noise due to human activities. Data blocks of several months of continuous gravity records have been collected over a time span of three years, together with the meteorological data. The gravimeter has been calibrated at relative accuracy better than 0.3% with the aid of a mobile mass system, by imposed perturbations of the local gravity field and recording the gravimeter response. The results of this calibration technique were checked by two comparison experiments with absolute gravimeters performed during this period: the first, in May 1994 with the aid of the symmetrical rise and fall gravimeter of the Institute of Metrology Colonnetti of Turin, and the second in October 1997 involving an FG5 absolute gravimeter of the Institute de Physique du Globe of Strasbourg. The gravimeter signal was analysed to compute a high precision tidal model for Brasimone site. Starting from a set of gravimetric and atmospheric pressure data of high quality, relative to 46 months of observation, we performed the tidal analysis using Eterna 3.2 software to compute amplitudes, gravimetric factors and phases of the main waves of the Tamura catalogue. Finally a comparison experiment between two of the STS-1/VBB broadband seismometers of the MedNet project network and the gravity records relative to the Balleny Islands earthquake (March 25, 1998) were analysed to look for evidence of normal modes due to the free oscillations of the Earth.

scholarly journals Glider Sampling Simulations in High-Resolution Ocean Models

2020 ◽  
Vol 37 (6) ◽  
pp. 975-992
Author(s):  
Jacob M. Steinberg ◽  
Charles C. Eriksen
Keyword(s):  
High Resolution ◽  
Velocity Profile ◽  
Numerical Models ◽  
Mesoscale Eddy ◽  
Normal Modes ◽  
Vertical Displacement ◽  
Geostrophic Velocity ◽  
Velocity Amplitude ◽  
The Difference ◽  
Autonomous Underwater Glider

AbstractIdealized simulations of autonomous underwater glider sampling along sawtooth vertical–horizontal paths are carried out in two high-resolution ocean numerical models to explore the accuracy of isopycnal vertical displacement and geostrophic velocity profile estimates. The effects of glider flight speed, sampling pattern geometry, and measurement noise on velocity profile accuracy are explored to interpret recent full-ocean-depth Deepglider observations and provide sampling recommendations for glider missions. The average magnitude of velocity error profiles, defined as the difference between simulated glider-sampled geostrophic velocity profile estimates and model velocity profiles averaged over the spatial and temporal extent of corresponding simulated glider paths, is less than 0.02 m s−1 over most of the water column. This accuracy and the accuracy of glider geostrophic shear profile estimates are dependent on the ratio of mesoscale eddy to internal wave velocity amplitude. Projection of normal modes onto full-depth vertical profiles of model and simulated glider isopycnal vertical displacement and geostrophic velocity demonstrates that gliders are capable of resolving barotropic and baroclinic structure through at least the eighth baroclinic mode.

A peek into Jupiter’s normal modes from Juno gravity data

2021 ◽  
Author(s):  
Daniele Durante ◽  
Luciano Iess
Keyword(s):  
Gravity Field ◽  
Gravity Data ◽  
Normal Modes ◽  
Integration Time ◽  
Interior Structure ◽  
Axially Symmetric ◽  
Error Sources ◽  
Physical Constraints ◽  
Doppler Data ◽  
Very High

<p>As of April 2021, Juno is close to complete its nominal mission, awaiting to enter its extended mission. Thanks to the extremely accurate Doppler data (having an accuracy as low as 10 micron/s at an integration time of 60 s) acquired during close perijove passes in the last 4 years, Juno provided an unprecedented view of Jupiter’s gravity field, which is crucial to determine its interior structure. In order to recover the gravity field of the planet, the orbits of Juno have to be reconstructed to a very high accuracy. The latest gravity field reconstruction showed hints to a non-static and/or non-axially symmetric field, possibly related to several different phenomena, such as normal modes, localized atmospheric or deeply-rooted dynamics. These tiny phenomena produces a residual signal at a level of few tens of micron/s in Juno Doppler data. To confidently study these tiny unconventional phenomena, the dynamical model of Juno’s spacecraft have been accurately characterized and possible error sources investigated and ruled out.</p><p>The focus of this study is Jupiter’s normal modes. Our main goal is to assess whether the residuals signatures can be explained by the gravitational disturbances induced by normal modes inside the planet, assuming reasonable physical constraints. Ground-based observations of Jupiter’ normal modes can be used as a guide.</p>

Jupiter’s gravity field updates from Juno

2020 ◽  
Author(s):  
Daniele Durante ◽  
Marzia Parisi ◽  
Daniele Serra ◽  
Marco Zannoni ◽  
Virginia Notaro ◽  
...  
Keyword(s):  
Gravity Field ◽  
Orbit Determination ◽  
Normal Modes ◽  
Precise Orbit Determination ◽  
Great Sensitivity ◽  
Integration Time ◽  
Axially Symmetric ◽  
Eccentric Orbit ◽  
Symmetric Field ◽  
Doppler Data

<p>The Juno spacecraft arrived at Jupiter’s system on July 4th, 2016 and reached the mid-point of its nominal mission in December 2018, after completing 17 perijove passes. Juno is currently orbiting Jupiter in a highly eccentric orbit, with a perijove altitude of about 4000 km that provides great sensitivity to the gravitational field of the planet. The radioscience instrumentation on board Juno enables very accurate radial velocity (Doppler) measurements, with noise as low as 10 micron/s at an integration time of 60 s. The gravity field of the planet is recovered though detailed reconstruction of Juno’s motion and observation model, performed with JPL’s and University of Pisa’s latest precise orbit determination codes, MONTE and ORBIT14 respectively.</p><p>We provide an update on Jupiter’s gravity field, its tidal response and spin axis motion over the first half of Juno’s mission. Although the Doppler data collected during the first two gravity-dedicated perijove passes have been reduced to the noise level by assuming a purely axially symmetric field for the gas giant, the current dataset, which includes ten passes, hints to a non-static and/or non-axially symmetric field, possibly related to several different mechanisms, such as normal modes, localized atmospheric or deeply-rooted dynamics.</p>

scholarly journals A Global Gravity Reconstruction Method for Mercury Employing Deep Convolutional Neural Network

2020 ◽  
Vol 12 (14) ◽  
pp. 2293
Author(s):  
Shuheng Zhao ◽  
Denghong Liu ◽  
Qiangqiang Yuan ◽  
Jie Li
Keyword(s):  
Neural Network ◽  
Spatial Structure ◽  
Gravity Field ◽  
Field Data ◽  
Gravity Data ◽  
Space Environment ◽  
Reconstruction Method ◽  
High Quality ◽  
Low Degree ◽  
High Degree

Mercury, the enigmatic innermost planet in the solar system, is one of the most important targets of space exploration. High-quality gravity field data are significant to refine the physical characterization of Mercury in planetary exploration missions. However, Mercury’s gravity model is limited by relatively low spatial resolution and stripe noises, preventing fine-scale analysis and applications. By analyzing Mercury’s gravity data and topography data in the 2D spatial field, we find they have fairly high spatial structure similarity. Based on this, in this paper, a novel convolution neural network (CNN) approach is proposed to improve the quality of Mercury’s gravity field data. CNN can extract the spatial structure features of gravity data and construct a nonlinear mapping between low- and high-degree data directly. From a low-degree gravity input, the corresponding initial high-degree result can be obtained. Meanwhile, the structure characteristics of the high-resolution digital elevation model (DEM) are extracted and fused to the initial data, to get the final stripe-free result with improved resolution. Given the paucity of Mercury’s data, high-quality lunar datasets are employed as pretraining data after verifying the spatial similarity between gravity and terrain data of the Moon. The HgM007 gravity field obtained by the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) mission at Mercury is selected for experiments to test the ability of the proposed algorithm to remove the stripes caused by quality differences of the highly eccentric orbit data. Experimental results show that our network can directly obtain stripe-free and higher-degree data via inputting low-degree data and implicitly assuming a lunar-like relation between crustal density and porosity. Albeit the CNN-based method cannot be sensitive to subsurface features not present in the initial dataset, it still provides a new perspective for the gravity field refinement.

One-dimensional ion-acoustic modes of bounded plasmas

1970 ◽  
Vol 4 (1) ◽  
pp. 195-203 ◽  
Author(s):  
Rui Rosa ◽  
J. E. Allen
Keyword(s):  
Spatial Structure ◽  
Normal Modes ◽  
Characteristic Frequencies ◽  
One Dimensional ◽  
Acoustic Modes ◽  
Ion Acoustic

One-dimensional ion-acoustic normal modes of bounded plasmas are theoretically investigated in plane, cylindrical and spherical geometries. The characteristic frequencies, damping constants and spatial structure of the oscillatory modes are obtained.

scholarly journals Spatial structure of unstable normal modes in a glass-forming liquid

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Masanari Shimada ◽  
Daniele Coslovich ◽  
Hideyuki Mizuno ◽  
Atsushi Ikeda
Keyword(s):  
Potential Energy ◽  
Spatial Structure ◽  
Potential Energy Surface ◽  
Mode Coupling ◽  
Energy Surface ◽  
Normal Modes ◽  
Stationary Points ◽  
Far Field ◽  
Local Minima ◽  
Glass Forming

The phenomenology of glass-forming liquids is often described in terms of their underlying, high-dimensional potential energy surface. In particular, the statistics of stationary points sampled as a function of temperature provides useful insight into the thermodynamics and dynamics of the system. To make contact with the real space physics, however, analysis of the spatial structure of the normal modes is required. In this work, we numerically study the potential energy surface of a glass-forming ternary mixture. Starting from liquid configurations equilibrated over a broad range of temperatures using a swap Monte Carlo method, we locate the nearby stationary points and investigate the spatial architecture and the energetics of the associated unstable modes. Through this spatially-resolved analysis, originally developed to study local minima, we corroborate recent evidence that the nature of the unstable modes changes from delocalized to localized around the mode-coupling temperature. We find that the displacement amplitudes of the delocalized modes have a slowly decaying far field, whereas the localized modes consist of a core with large displacements and a rapidly decaying far field. The fractal dimension of unstable modes around the mobility edge is equal to 1, consistent with the scaling of the participation ratio. Finally, we find that around and below the mode-coupling temperature the unstable modes are localized around structural defects, characterized by a disordered local structure markedly different from the liquid's locally favored structure. These defects are similar to those associated to quasi-localized vibrations in local minima and are good candidates to predict the emergence of localized excitations at low temperature.

Clean Electron Microscope Substrate Films Used for Micrometeorite Collection and Study

1967 ◽  
Vol 25 ◽  
pp. 366-367
Author(s):  
D. M. Davies ◽  
R. Kemner ◽  
E. F. Fullam
Keyword(s):  
Thin Film ◽  
Electron Microscope ◽  
High Altitude ◽  
Amyl Acetate ◽  
Temperature Variations ◽  
Film Forming ◽  
Film Specimen ◽  
Particulate Contaminants

All serious electron microscopists at one time or another have been concerned with the cleanliness and freedom from artifacts of thin film specimen support substrates. This is particularly important where there are relatively few particles of a sample to be found for study, as in the case of micrometeorite collections. For the deposition of such celestial garbage through the use of balloons, rockets, and aircraft, the thin film substrates must have not only all the attributes necessary for use in the electron microscope, but also be able to withstand rather wide temperature variations at high altitude, vibration and shock inherent in the collection vehicle's operation and occasionally an unscheduled violent landing.Nitrocellulose has been selected as a film forming material that meets these requirements yet lends itself to a relatively simple clean-up procedure to remove particulate contaminants. A 1% nitrocellulose solution is prepared by dissolving “Parlodion” in redistilled amyl acetate from which all moisture has been removed.

Contributions of Voice and Nonverbal Communication to Perceived Masculinity–Femininity for Cisgender and Transgender Communicators

2020 ◽  
Vol 63 (4) ◽  
pp. 931-947
Author(s):  
Teresa L. D. Hardy ◽  
Carol A. Boliek ◽  
Daniel Aalto ◽  
Justin Lewicke ◽  
Kristopher Wells ◽  
...  
Keyword(s):  
Fundamental Frequency ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Vocal Tract ◽  
Presentation Mode ◽  
Pressure Level ◽  
Presentation Modes ◽  
Audiovisual Stimuli ◽  
Vocal Tract Resonance ◽  
Point Light

Purpose The purpose of this study was twofold: (a) to identify a set of communication-based predictors (including both acoustic and gestural variables) of masculinity–femininity ratings and (b) to explore differences in ratings between audio and audiovisual presentation modes for transgender and cisgender communicators. Method The voices and gestures of a group of cisgender men and women ( n = 10 of each) and transgender women ( n = 20) communicators were recorded while they recounted the story of a cartoon using acoustic and motion capture recording systems. A total of 17 acoustic and gestural variables were measured from these recordings. A group of observers ( n = 20) rated each communicator's masculinity–femininity based on 30- to 45-s samples of the cartoon description presented in three modes: audio, visual, and audio visual. Visual and audiovisual stimuli contained point light displays standardized for size. Ratings were made using a direct magnitude estimation scale without modulus. Communication-based predictors of masculinity–femininity ratings were identified using multiple regression, and analysis of variance was used to determine the effect of presentation mode on perceptual ratings. Results Fundamental frequency, average vowel formant, and sound pressure level were identified as significant predictors of masculinity–femininity ratings for these communicators. Communicators were rated significantly more feminine in the audio than the audiovisual mode and unreliably in the visual-only mode. Conclusions Both study purposes were met. Results support continued emphasis on fundamental frequency and vocal tract resonance in voice and communication modification training with transgender individuals and provide evidence for the potential benefit of modifying sound pressure level, especially when a masculine presentation is desired.

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