446 research outputs found
Calibration of the angular momenta of the minor planets in the solar system
We aim to determine the relative angle between the total angular momentum of
the minor planets and that of the Sun-planets system, and to improve the
orientation of the invariable plane of the solar system. By utilizing physical
parameters available in public domain archives, we assigned reasonable masses
to 718041 minor planets throughout the solar system, including near-Earth
objects, main belt asteroids, Jupiter trojans, trans-Neptunian objects,
scattered-disk objects, and centaurs. Then we combined the orbital data to
calibrate the angular momenta of these small bodies, and evaluated the specific
contribution of the massive dwarf planets. The effects of uncertainties on the
mass determination and the observational incompleteness were also estimated. We
determine the total angular momentum of the known minor planets to be
g cm s. The relative angle
between this vector and the total angular momentum of the Sun-planets
system is calculated to be 14.74 deg.. By excluding the dwarf planets Eris,
Pluto, and Haumea, which have peculiar angular momentum directions,
drops sharply to 1.76 deg.; a similar result applies to each individual minor
planet group. This suggests that, without these three most massive bodies, the
plane perpendicular to the total angular momentum of the minor planets would be
close to the invariable plane of the solar system. On the other hand, the
inclusion of Eris, Haumea, and Makemake can produce a difference of 1254 mas in
the inclination of the invariable plane, which is much larger than the
difference of 9 mas induced by Ceres, Vesta, and Pallas as found previously. By
taking into account the angular momentum contributions from all minor planets,
including unseen ones, the orientation improvement of the invariable plane is
larger than 1000 mas in inclination with a error of 50-140 mas.Comment: 10 pages, 3 figures, published in A&
Link Travel Time Estimation in Double-Queue-Based Traffic Models
Double queue concept has gained its popularity in dynamic user equilibrium (DUE) modeling because it can properly model real traffic dynamics. While directly solving such double-queue-based DUE problems is extremely challenging, an approximation scheme called first-order approximation was proposed to simplify the link travel time estimation of DUE problems in a recent study without evaluating its properties and performance. This paper focuses on directly investigating the First-In-First-Out property and the performance of the first-order approximation in link travel time estimation by designing and modeling dynamic network loading (DNL) on single-line stretch networks. After model formulation, we analyze the First-In-First-Out (FIFO) property of the first-order approximation. Then a series of numerical experiments is conducted to demonstrate the FIFO property of the first-order approximation, and to compare its performance with those using the second-order approximation, a point queue model, and the cumulative inflow and exit flow curves. The numerical results show that the first-order approximation does not guarantee FIFO and also suggest that the second-order approximation is recommended especially when the link exit flow is increasing. The study provides guidance for further study on proposing new methods to better estimate link travel times
The invasion of a free floating planet and the number asymmetry of Jupiter Trojans
This paper extends our previous study (Li et al. 2023) of the early evolution
of Jupiter and its two Trojan swarms by introducing the possible perturbations
of a free floating planet (FFP) invading the Solar System. In the framework of
the invasion of a FFP, we aim to provide some new scenarios to explain the
number asymmetry of the L4 and L5 Jupiter Trojans, and some other observed
features. We investigate two different cases: (i) The indirect case, where
Jupiter experiences a scattering encounter with the FFP and jumps outwards at a
speed that is much higher than that considered in(Li et al. 2023), resulting in
a change in the numbers of the L4 (N4) and L5 (N5) Trojans swarms. (ii) The
direct case, in which the FFP traverses the L5 region and affects the stability
of the local Trojans. In the indirect case, the outward migration of Jupiter
can be fast enough to make the L4 islands disappear temporarily, inducing a
resonant amplitude increase of the local Trojans. After the migration is over,
the L4 Trojans come back to the re-appeared and enlarged islands. As for the L5
islands, they always exist but expand even more considerably. Since the L4
swarm suffers less excitation in the resonant amplitude than the L5 swarm, more
L4 Trojans are stable and could survive to the end. In the direct case, the FFP
could deplete a considerable fraction of the L5 Trojans, while the L4 Trojans
at large distances are not affected and all of them could survive. Both the
indirect and direct cases could result in a number ratio of R45=N4/N5~1.6 that
can potentially explain the current observations. The latter has the advantage
of producing the observed resonant amplitude distribution. For achieving these
results, we propose that the FFP should have a mass of at least of a few tens
of Earth masses and its orbital inclination is allowed to be as high as 40
degrees.Comment: Accepted for publication in A&A, 13 pages, 7 figures, 5 table
Large-step neural network for learning the symplectic evolution from partitioned data
In this study, we focus on learning Hamiltonian systems, which involves
predicting the coordinate (q) and momentum (p) variables generated by a
symplectic mapping. Based on Chen & Tao (2021), the symplectic mapping is
represented by a generating function. To extend the prediction time period, we
develop a new learning scheme by splitting the time series (q_i, p_i) into
several partitions. We then train a large-step neural network (LSNN) to
approximate the generating function between the first partition (i.e. the
initial condition) and each one of the remaining partitions. This partition
approach makes our LSNN effectively suppress the accumulative error when
predicting the system evolution. Then we train the LSNN to learn the motions of
the 2:3 resonant Kuiper belt objects for a long time period of 25000 yr. The
results show that there are two significant improvements over the neural
network constructed in our previous work (Li et al. 2022): (1) the conservation
of the Jacobi integral, and (2) the highly accurate predictions of the orbital
evolution. Overall, we propose that the designed LSNN has the potential to
considerably improve predictions of the long-term evolution of more general
Hamiltonian systems.Comment: 13 pages, 7 figures, accepted for publication in MNRA
Asymmetry in the number of L4 and L5 Jupiter Trojans driven by jumping Jupiter
Context. More than 10000 Jupiter Trojans have been detected so far. They are
moving around the L4 and L5 triangular Lagrangian points of the Sun-Jupiter
system and their distributions can provide important clues to the early
evolution of the Solar System.
Aims. The number asymmetry of the L4 and L5 Jupiter Trojans is a longstanding
problem. We aim to test a new mechanism in order to explain this anomalous
feature by invoking the jumping-Jupiter scenario.
Methods. First, we introduce the orbital evolution of Jupiter caused by the
giant planet instability in the early Solar System. In this scenario, Jupiter
could undergo an outward migration at a very high speed. We then investigate
how such a jump changes the numbers of the L4 (N4) and L5 (N5) Trojans.
Results. The outward migration of Jupiter can distort the co-orbital orbits
near the Lagrangian points, resulting in L4 Trojans being more stable than the
L5 ones. We find that, this mechanism could potentially explain the unbiased
number asymmetry of N4/N5~1.6 for the known Jupiter Trojans. The uncertainties
of the system parameters, e.g. Jupiter's eccentricity and inclination, the
inclination distribution of Jupiter Trojans, are also taken into account and
our results about the L4/L5 asymmetry have been further validated. However, the
resonant amplitudes of the simulated Trojans are excited to higher values
compared to the current population. A possible solution is that collisions
among the Trojans may reduce their resonant amplitudes.Comment: 11 pages, 5 figures, accepted for publication in A&
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Geochemical characterization of shallow groundwater at the Cranfield aquifer and numerical simulation: Can pH and carbonate parameters be used to detect potential CO2 leakage at geological CO2 sequestration sites?
Bureau of Economic Geolog
Spatially resolved Spectro-photometry of M81: Age, Metallicity and Reddening Maps
In this paper, we present a multi-color photometric study of the nearby
spiral galaxy M81, using images obtained with the Beijing Astronomical
Observatory 60/90 cm Schmidt Telescope in 13 intermediate-band filters from
3800 to 10000{\AA}. The observations cover the whole area of M81 with a total
integration of 51 hours from February 1995 to February 1997. This provides a
multi-color map of M81 in pixels of 1\arcsec.7 \times 1\arcsec.7. Using
theoretical stellar population synthesis models, we demonstrate that some BATC
colors and color indices can be used to disentangle the age and metallicity
effect. We compare in detail the observed properties of M81 with the
predictions from population synthesis models and quantify the relative chemical
abundance, age and reddening distributions for different components of M81. We
find that the metallicity of M81 is about with no significant
difference over the whole galaxy. In contrast, an age gradient is found between
stellar populations of the central regions and of the bulge and disk regions of
M81: the stellar population in its central regions is older than 8 Gyr while
the disk stars are considerably younger, Gyr. We also give the
reddening distribution in M81. Some dust lanes are found in the galaxy bulge
region and the reddening in the outer disk is higher than that in the central
regions.Comment: Accepted for publication in AJ (May 2000 issue). 27 pages including 6
figures. Uses AASTeX aasms4 styl
Identification of a Cell-of-Origin for Fibroblasts Comprising the Fibrotic Reticulum in Idiopathic Pulmonary Fibrosis
Idiopathic pulmonary fibrosis (IPF) is a progressive disease of the middle aged and elderly with a prevalence of one million persons worldwide. The fibrosis spreads from affected alveoli into contiguous alveoli, creating a reticular network that leads to death by asphyxiation. Lung fibroblasts from patients with IPF have phenotypic hallmarks, distinguishing them from their normal counterparts: pathologically activated Akt signaling axis, increased collagen and α-smooth muscle actin expression, distinct gene expression profile, and ability to form fibrotic lesions in model organisms. Despite the centrality of these fibroblasts in disease pathogenesis, their origin remains uncertain. Here, we report the identification of cells in the lungs of patients with IPF with the properties of mesenchymal progenitors. In contrast to progenitors isolated from nonfibrotic lungs, IPF mesenchymal progenitor cells produce daughter cells manifesting the full spectrum of IPF hallmarks, including the ability to form fibrotic lesions in zebrafish embryos and mouse lungs, and a transcriptional profile reflecting these properties. Morphological analysis of IPF lung tissue revealed that mesenchymal progenitor cells and cells with the characteristics of their progeny comprised the fibrotic reticulum. These data establish that the lungs of patients with IPF contain pathological mesenchymal progenitor cells that are cells of origin for fibrosis-mediating fibroblasts. These fibrogenic mesenchymal progenitors and their progeny represent an unexplored target for novel therapies to interdict fibrosis
An Integrative Model for Soil Biogeochemistry and Methane Processes: I. Model Structure and Sensitivity Analysis
Environmental changes are anticipated to generate substantial impacts on carbon cycling in peatlands, affecting terrestrial-climate feedbacks. Understanding how peatland methane (CH4) fluxes respond to these changing environments is critical for predicting the magnitude of feedbacks from peatlands to global climate change. To improve predictions of CH4 fluxes in response to changes such as elevated atmospheric CO2 concentrations and warming, it is essential for Earth system models to include increased realism to simulate CH4 processes in a more mechanistic way. To address this need, we incorporated a new microbial-functional group-based CH4 module into the Energy Exascale Earth System land model (ELM) and tested it with multiple observational data sets at an ombrotrophic peatland bog in northern Minnesota. The model is able to simulate observed land surface CH4 fluxes and fundamental mechanisms contributing to these throughout the soil profile. The model reproduced the observed vertical distributions of dissolved organic carbon and acetate concentrations. The seasonality of acetoclastic and hydrogenotrophic methanogenesisâtwo key processes for CH4 productionâand CH4 concentration along the soil profile were accurately simulated. Meanwhile, the model estimated that plant-mediated transport, diffusion, and ebullition contributed to âŒ23.5%, 15.0%, and 61.5% of CH4 transport, respectively. A parameter sensitivity analysis showed that CH4 substrate and CH4 production were the most critical mechanisms regulating temporal patterns of surface CH4 fluxes both under ambient conditions and warming treatments. This knowledge will be used to improve Earth system model predictions of these high-carbon ecosystems from plot to regional scales
A survey and classification of storage deduplication systems
The automatic elimination of duplicate data in a storage system commonly known as deduplication is increasingly accepted as an effective technique to reduce storage costs. Thus, it has been applied to different storage types, including archives and backups, primary storage, within solid state disks, and even to random access memory. Although the general approach to deduplication is shared by all storage types, each poses specific challenges and leads to different trade-offs and solutions. This diversity is often misunderstood, thus underestimating the relevance of new research and development.
The first contribution of this paper is a classification of deduplication systems according to six criteria that correspond to key design decisions: granularity, locality, timing, indexing, technique, and scope.
This classification identifies and describes the different approaches used for each of them. As a second contribution, we describe which combinations of these design decisions have been proposed and found more useful for challenges in each storage type. Finally, outstanding research challenges and unexplored design points are identified and discussed.This work is funded by the European Regional Development Fund (EDRF) through the COMPETE Programme (operational programme for competitiveness) and by National Funds through the Fundacao para a Ciencia e a Tecnologia (FCT; Portuguese Foundation for Science and Technology) within project RED FCOMP-01-0124-FEDER-010156 and the FCT by PhD scholarship SFRH-BD-71372-2010
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