Is IMU-Based Center of Mass Estimation Reliable? Preliminary Study in Perturbed Conditions

Context. Gaia Data Release 2 (DR2) includes milliarcsecond-accuracy astrometry for 14 099 asteroids. One of the main expected scientific applications of these data is asteroid mass estimation via the modeling of perturbations during asteroid-asteroid encounters. Aims. We explore the practical impact of the Gaia astrometry of asteroids for the purpose of asteroid mass and orbit estimation by estimating the masses individually for four large asteroids. We use various combinations of Gaia astrometry and/or Earth-based astrometry so as to determine the impact of Gaia on the estimated masses. By utilizing published information about estimated volumes and meteorite analogs, we also derive estimates for bulk densities and macroporosities. Methods. We apply a Markov chain Monte Carlo (MCMC) algorithm for asteroid mass and orbit estimation by modeling asteroid-asteroid close encounters to four separate large asteroids in an attempt to estimate their masses based on multiple simultaneously studied close encounters with multiple test asteroids. In order to validate our algorithm and data treatment, we apply the MCMC algorithm to pure orbit determination for the main-belt asteroid (367) Amicitia and compare the residuals to previously published ones. In addition, we attempt to estimate a mass for (445) Edna with Gaia astrometry alone based on its close encounter with (1764) Cogshall. Results. In the case of the orbit of (367) Amicitia, we find a solution that improves on the previously published solution. The study of (445) Edna reveals that mass estimation with DR2 astrometry alone is unfeasible and that it must be combined with astrometry from other sources to achieve meaningful results. We find that a combination of DR2 and Earth-based astrometry results in dramatically reduced uncertainties and, by extension, significantly improved results in comparison to those computed based on less accurate Earth-based astrometry alone. Conclusions. Our mass estimation algorithm works well with a combination of Gaia DR2 and Earth-based astrometry and provides very impressive results with significantly reduced uncertainties. We note that the DR2 has a caveat in that many asteroids suitable for mass-estimation purposes are not included in the relatively small sample. This limits the number of asteroids to which mass estimation can be applied. However, this issue will largely be corrected with the forthcoming third Gaia data release, which is expected to allow for a wave of numerous accurate mass estimates for a wide range of asteroids.

A statistically rigorous approach for determining likely errors on estimates of mass and volume change in metasomatic systems is presented and then used to assess mass transfer resulting from hydrothermal alteration of marble during regional metamorphism. Analysis of metasomatic effects using standard statistical methods designed for unconstrained, univariant data often fails to provide useful results for several important reasons:1. The concentration of any constituent in a composition is constrained to be between 0 and 100 wt percent.2. The sum of the concentrations of all constituents must be 100 wt percent (the closure constraint). Compositions are multivariate and provide information only about the relative proportions of constituents.3. The maximum possible mass or volume loss is -100 percent (-100% corresponds to complete mass or volume loss).4. Rock bulk density must be greater than 0 g cm (super -3) .5. The underlying probability distributions for mass and volume changes are commonly non-normal.To address these issues, we use statistical procedures recently developed to treat the special properties of compositional data, including closure, and the bootstrap method to compute accurate confidence intervals for assessing how far in error best estimates of mass and volume change are likely to be. The bootstrap deals effectively with non-normality and constraints (1), (3), and (4).We apply our approach to gain a better understanding of synmetamorphic (Acadian orogeny) hydrothermal alteration of upper greenschist facies and amphibolite facies marble beds of the Wepawaug Schist, Connecticut. The marbles lost significant amounts of volatiles (dominantly CO 2 and H 2 O), Si, Ti, K, Rb, Sr, and Ba. Best estimates of total mass and volume change are -27 and -32 percent, respectively. The bulk of the lost mass was volatiles ( approximately 140 g kg (super -1) ), SiO 2 ( approximately 60 g kg (super -1) ), and K 2 O ( approximately 15 g kg (super -1) ) (numbers are g lost per kg of parent rock). Volatile loss was probably regional in scope. Loss of Si, Ti, K, Rb, Sr, and Ba occurred over minimum length scales on the order of typical hand sample dimensions; maximum length scales remain to be determined.The FORTRAN 77 computer code that performs the calculations described herein is available from the senior author.

The aim of the present paper is to quantify the dependence of the estimates of luminosities and stellar mass content of early-type galaxies on the different models and model parameters which can be used to analyse the observational data. The paper is organized in two parts. The first one analyses the dependence of the M/C ratios and of the k-corrections in different bands on model parameters (initial mass function, metallicity, star formation history, age), assuming some among the most popular spectrophotometric codes usually adopted to study the evolutionary status of galaxies: Bruzual & Charlot (BC03), Charlot & Bruzual (CB08), Maraston (Ma05), Fioc & Rocca-Volmerange (PEGASE), Silva et al. (GRASIL). The second part of our work is dedicated to quantify the reliability and systematics affecting the mass and luminosity estimates obtained by means of the best-fitting technique applied to the photometric spectral energy distributions (SEDs) of early-type galaxies at 1 < z < 2. To this end, we apply the best-fitting technique to some mock catalogues built on the basis of a wide set of models of early-type galaxies. We then compare the luminosity and the stellar mass estimated from the SED fitting with the true known input values. The goodness of the mass estimate is found to be dependent on the mass estimator adopted to derive it, but masses cannot anyhow be retrieved better than within a factor of 2-3, depending on the quality of the available photometric data and/or on the distance of the galaxies since more distant galaxies are fainter on average and thus affected by larger photometric errors. Finally, we present a new empirical mass estimator based on the K-band apparent magnitude and on the observed (V - K) colour. We show that the reliability of the stellar mass content derived with this new estimator for early-type galaxies and its stability are even higher than those achievable with the best classic estimators, with the not negligible advantage that it does not need any multiwavelength data fitting.

We present single-epoch black hole mass (M BH) estimators based on the rest-frame ultraviolet (UV) Mg ii 2798 Å and optical Hβ 4861 Å emission lines. To enlarge the luminosity range of active galactic nuclei (AGNs), we combine the 31 reverberation-mapped AGNs with relatively low luminosities from Bahk et al., 47 moderate-luminosity AGNs from Woo et al., and 425 high-luminosity AGNs from the Sloan Digital Sky Survey. The combined sample has a monochromatic luminosity at 5100 Å in the range erg s−1, over the range 5.5 &lt; log(M BH/M ⊙) &lt; 9.5. Based on the fiducial mass from the line dispersion or FWHM of Hβ paired with the continuum luminosity at 5100 Å, we calibrate the best-fit parameters in the black hole mass estimators using the Mg ii line. We find that the differences in the line profiles between Mg ii and Hβ have significant effects on calibrating the UV M BH estimators. By exploring the systematic discrepancy between the UV and optical M BH estimators as a function of AGN properties, we suggest adding a correction term in the equation for the UV mass estimator. We also find a ∼0.1 dex bias in the M BH estimation due to the difference in the spectral slope in the range 2800–5200 Å. Depending on whether the selection of M BH estimator is based on either line dispersion or FWHM and either continuum or line luminosity, the derived UV mass estimators show ≳0.1 dex intrinsic scatter with respect to the fiducial Hβ-based M BH.

Postharvest citrus mass and size estimation using a logistic classification model and a watershed algorithm

We present a new approach (MADE) that generates mass, age, and distance estimates of red giant stars from a combination of astrometric, photometric, and spectroscopic data. The core of the approach is a Bayesian artificial neural network (ANN) that learns from and completely replaces stellar isochrones. The ANN is trained using a sample of red giant stars with mass estimates from asteroseismology. A Bayesian isochrone pipeline uses the astrometric, photometric, spectroscopic, and asteroseismology data to determine posterior distributions for the training outputs: mass, age, and distance. Given new inputs, posterior predictive distributions for the outputs are computed, taking into account both input uncertainties, and uncertainties in the ANN parameters. We apply MADE to ${\sim }10\, 000$ red giants in the overlap between the 14th data release from the APO Galactic Evolution Experiment (APOGEE) and the Tycho-Gaia astrometric solution (TGAS). The ANN is able to reduce the uncertainty on mass, age, and distance estimates for training-set stars with high output uncertainties allocated through the Bayesian isochrone pipeline. The fractional uncertainties on mass are $\lt 10{{\ \rm per\ cent}}$ and on age are between 10 to $25{{\ \rm per\ cent}}$. Moreover, the time taken for our ANN to predict masses, ages, and distances for the entire catalogue of APOGEE-TGAS stars is of a similar order of the time taken by the Bayesian isochrone pipeline to run on a handful of stars. Our resulting catalogue clearly demonstrates the expected thick- and thin-disc components in the [M/H]–[α/M] plane, when examined by age.

Vehicle mass estimation is the key technology to improve vehicle stability. However, the existing mass estimation accuracy is easily affected by the change of road gradient, and there are few studies on the mass estimation method of the light truck. Aiming at this problem, this paper uses sensors to measure road gradient and rear suspension deformation and proposes a sensor-based vehicle mass estimation algorithm. First, factors that affect the mass estimation are analyzed, road gradient error correction method and mass estimation error correction method are established. Besides, the suspension deformation is decoupled from the road gradient. Second, the mass estimation algorithm model was established in Matlab/Simulink platform and compared with the mass estimation iterative algorithm. Finally, the road test was carried out under various conditions, the results show that the proposed mass estimation algorithm is robust, and the accuracy of the mass estimation will not be affected by the sudden change of road gradient.

&lt;div class="htmlview paragraph"&gt;This paper describes an effective integrated method for estimation of subject-specific mass, inertia tensor, and center of mass of individual body segments of a digital avatar for use with physics-based digital human modeling simulation environment. One of the main goals of digital human modeling and simulation environments is that a user should be able to change the avatar (from male to female to a child) at any given time. The user should also be able to change the various link dimensions, like lengths of upper and lower arms, lengths of upper and lower legs, etc. These customizations in digital avatar's geometry change the kinematic and dynamic properties of various segments of its body. Hence, the mass and center of mass/inertia data of the segments must be updated before simulating physics-based realistic motions. Most of the current methods use mass and inertia properties calculated from a set of regression equations based on average of some population. In this paper, we calculate avatar-specific mass and inertia properties from the scans of digital human. The mesh of the digital human model is split using equations defined by a plane at each joint. The equation is used to split up the geometry. The resultant geometry is closed to make the mesh hole free. Mass, center of mass (assuming uniform density) and inertia tensor are then calculated using the method described in the paper (Mirtich 1996). The method can be used in all physics-based digital human modeling and simulation software where the scan of the avatar is available. The use of mass inertia properties calculated by this method enables users to customize digital avatar and simulate motions for specifically for that avatar.&lt;/div&gt;

Aims.We aim to perform a theoretical evaluation of the impact of the mass loss indetermination on asteroseismic grid based estimates of masses, radii, and ages of stars in the red giant branch (RGB) phase.Methods.We adopted the SCEPtER pipeline on a grid spanning the mass range [0.8; 1.8]M⊙. As observational constraints, we adopted the star effective temperatures, the metallicity [Fe/H], the average large frequency spacing Δν,and the frequency of maximum oscillation powerνmax. The mass loss was modelled following a Reimers parametrization with the two different efficienciesη= 0.4 andη= 0.8.Results.In the RGB phase, the average random relative error (owing only to observational uncertainty) on mass and age estimates is about 8% and 30% respectively. The bias in mass and age estimates caused by the adoption of a wrong mass loss parameter in the recovery is minor for the vast majority of the RGB evolution. The biases get larger only after the RGB bump. In the last 2.5% of the RGB lifetime the error on the mass determination reaches 6.5% becoming larger than the random error component in this evolutionary phase. The error on the age estimate amounts to 9%, that is, equal to the random error uncertainty. These results are independent of the stellar metallicity [Fe/H] in the explored range.Conclusions.Asteroseismic-based estimates of stellar mass, radius, and age in the RGB phase can be considered mass loss independent within the range (η∈ [0.0,0.8]) as long as the target is in an evolutionary phase preceding the RGB bump.

The white dwarf mass-radius relationship is fundamental to modern astrophysics. It is central to routine estimation of DA white dwarf masses derived from spectroscopic temperatures and gravities. It is also the basis for observational determinations of the white dwarf initial-final mass relation. Nevertheless, definitive and detailed observational confirmations of the mass-radius relation (MRR) remain elusive due to a lack of sufficiently accurate white dwarf masses and radii. Current best estimates of masses and radii allow only broad conclusions about the expected inverse relation between masses and radii in degenerate stars. In this paper we examine a restricted set of 12 DA white dwarf binary systems for which accurate (1) trigonometric parallaxes, (2) spectroscopic effective temperatures and gravities, and (3) gravitational redshifts are available. We consider these three independent constraints on mass and radius in comparison with an appropriate evolved MRR for each star. For the best-determined systems it is found that the DA white dwarfs conform to evolved theoretical MRRs at the 1-{\sigma} to 2-{\sigma} level. For the white dwarf 40 Eri B (WD0413-077) we find strong evidence for the existence of a "thin" hydrogen envelope. For other stars improved parallaxes will be necessary before meaningful comparisons are possible. For several systems current parallaxes approach the precision required for the state-of-the-art mass and radius determinations that will be obtained routinely from the Gaia mission. It is demonstrated here how these anticipated results can be used to firmly constrain details of theoretical mass-radius determinations.

Statistical Study of the Unfolding of Multimodular Proteins and their Energy Landscape by Atomic Force Microscopy

The kHz quasi‐periodic oscillations (QPOs) have been detected by the RXTE satellite in about thirty neutron stars (NSs) in low mass X‐ray binaries (LMXBs), which are usually interpreted to be related to the Keplerian motions in the orbit close to NS surface where the accreted matter is sucked onto the star. Based on the MHD Alfvén wave oscillation model and the relativistic precession model for the neutron star (NS) kHz QPOs, estimations of mass M and radius R of some NSs are given, which can give clues to evaluate the models. Furthermore, comparisons with theoretical M ‐R relations by stellar equations of state (EOSs) are presented (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Size, Mass and Density of Asteroids (SiMDA) - A Web Based Archive and Data Service

Context. The mass of protoplanetary disks is arguably one of their most important quantities shaping their evolution toward planetary systems, but it remains a challenge to determine this quantity. Using the high spatial resolution now available on telescopes such as the Atacama Large Millimeter/submillimeter Array (ALMA), recent studies derived a relation between the disk surface density and the location of the “dust lines”. This is a new concept in the field, linking the disk size at different continuum wavelengths with the radial distribution of grain populations of different sizes. Aims. We aim to use a dust evolution model to test the dependence of the dust line location on disk gas mass. In particular, we are interested in the reliability of the method for disks showing radial substructures, as recent high-resolution observations revealed. Methods. We performed dust evolution calculations, which included perturbations to the gas surface density with different amplitudes at different radii, to investigate their effect on the global drift timescale of dust grains. These models were then used to calibrate the relation between the dust grain drift timescale and the disk gas mass. We investigated under which condition the dust line location is a good mass estimator and tested how different stellar and disk properties (disk mass, stellar mass, disk age, and dust-to-gas ratio) affect the dust line properties. Finally, we show the applicability of this method to disks such as TW Hya and AS 209 that have been observed at high angular resolution with ALMA and show pronounced disk structures. Results. Our models without pressure bumps confirm a strong dependence of the dust line location on the disk gas mass and its applicability as a reliable mass estimator. The other disk properties do not significantly affect the dust line location, except for the age of the system, which is the major source of uncertainty for this mass estimator. A population of synthetic disks was used to calibrate an analytic relation between the dust line location and the disk mass for smooth disks, finding that previous mass estimates based on dust lines overestimate disk masses by about one order of magnitude. Radial pressure bumps can alter the location of the dust line by up to ~10 au, while its location is mainly determined by the disk mass. Therefore, an accurate mass estimation requires a proper evaluation of the effect of bumps. However, when radial substructures act as traps for dust grains, the relation between the dust line location and disk mass becomes weaker, and other mass estimators need to be adopted. Conclusions. Our models show that the determination of the dust line location is a promising approach to the mass estimate of protoplanetay disks, but the exact relation between the dust line location and disk mass depends on the structure of the particular disk. We calibrated the relation for disks without evidence of radial structures, while for more complex structures we ran a simple dust evolution model. However, this method fails when there is evidence of strong dust traps. It is possible to reveal when dust evolution is dominated by traps, providing the necessary information for when the method should be applied with caution.

&lt;div&gt;This study presents the development and integration of a vehicle mass estimator into the ZF’s Adaptive Cruise Control (ACC) system. The aim is to improve the accuracy of the ACC system’s torque control for achieving desired speed and acceleration. Accurate mass estimation is critical for optimal control performance, particularly in commercial vehicles with variable loads. The incorporation of such mass estimation algorithm into the ACC system leads to significant reductions in the error between requested and measured acceleration during both flat and uphill driving conditions, with or without a preceding vehicle. The article details the estimator’s development, integration, and validation through comprehensive experimental testing. An electric front-wheel drive van was used. The vehicle’s longitudinal dynamics were modeled using D’Alembert’s principle to develop the mass estimation algorithm. This algorithm updates the mass estimate based on specific conditions: zero brake torque, high longitudinal acceleration, minimal slope, adequate speed, minimal wheel slip, and low yaw rate. These conditions ensure accurate mass estimation by minimizing the effects of nonlinearities and external disturbances. Experimental results showed that the mass estimator converges to the actual mass value as more samples are collected. Tests with varying loads confirmed the estimator’s accuracy, achieving a maximum absolute error of 72 kg and a percentage error of 1.71 %. When integrated into the ACC system, the estimated mass improved the control accuracy, especially in acceleration phases, reducing the time to reach the desired speed. Both cruise control and follow control tests, performed on flat and uphill roads, demonstrated that the ACC system with the mass estimator achieved the desired acceleration more accurately than without it. This improved the overall responsiveness and comfort of the ACC system under different driving conditions. The findings highlight the importance of accurate mass estimation for enhancing adaptive vehicle control technologies, representing a significant advancement in ACC systems.&lt;/div&gt;