361 research outputs found
Dynamical rearrangement of super-Earths during disk dispersal I. Outline of the magnetospheric rebound model
The Kepler mission has discovered that multiple close-in super-Earth planets
are common around solar-type stars, but their period ratios do not show strong
pile-ups near mean motion resonances (MMRs). One scenario is that super-Earths
form in a gas-rich disk, and they interact gravitationally with the surrounding
gas, inducing their orbital migration. Disk migration theory predicts, however,
that planets would end up at resonant orbits due to their differential
migration speed. Motivated by the discrepancy between observation and theory,
we seek for a mechanism that moves planets out of resonances. We examine the
orbital evolution of planet pairs near the magnetospheric cavity during the gas
disk dispersal phase. Our study determines the conditions under which planets
can escape resonances. We perform two-planet N-body simulations, varying the
planet masses, stellar magnetic field strengths, disk accretion rates and gas
disk depletion timescales. As planets migrate outward with the expanding
magnetospheric cavity, their dynamical configurations can be rearranged.
Migration of planets is substantial (minor) in a massive (light) disk. When the
outer planet is more massive than the inner planet, the period ratio of two
planets increases through outward migration. On the other hand, when the inner
planet is more massive, the final period ratio tends to remain similar to the
initial one. Larger stellar magnetic field strengths result in planets stopping
their migration at longer periods. We highlight \textit{magnetospheric rebound}
as an important ingredient able to reconcile disk migration theory with
observations. Even when planets are trapped into MMR during the early gas-rich
stage, subsequent cavity expansion would induce substantial changes to their
orbits, moving them out of resonance.Comment: 10 pages, 5 figures, accepted for publication in A&
Migration and Growth of Protoplanetary Embryos I: Convergence of Embryos in Protoplanetary Disks
According to the core-accretion scenario, planets form in protostellar disks
through the condensation of dust, coagulation of planetesimals, and emergence
of protoplanetary embryos. At a few AU in a minimum mass nebula, embryos'
growth is quenched by dynamical isolation due to the depletion of planetesimals
in their feeding zone. However, embryos with masses () in the range of a
few Earth masses () migrate toward a transition radius between the
inner viscously heated and outer irradiated regions of their natal disk. Their
limiting isolation mass increases with the planetesimals surface density. When
, embryos efficiently accrete gas and evolve into cores of
gas giants. We use numerical simulation to show that, despite streamline
interference, convergent embryos essentially retain the strength of
non-interacting embryos' Lindblad and corotation torque by their natal disks.
In disks with modest surface density (or equivalently accretion rates), embryos
capture each other in their mutual mean motion resonances and form a convoy of
super Earths. In more massive disks, they could overcome these resonant
barriers to undergo repeated close encounters including cohesive collisions
which enable the formation of massive cores.Comment: 9 pages, 6 figures, accepted for publication in Ap
Mechanism Design for Efficient Nash Equilibrium in Oligopolistic Markets
This paper investigates the efficiency loss in social cost caused by strategic bidding behavior of individual participants in a supply-demand balancing market, and proposes a mechanism to fully recover equilibrium social optimum via subsidization and taxation. We characterize the competition among supply-side firms to meet given inelastic demand, with linear supply function bidding and the proposed efficiency recovery mechanism. We show that the Nash equilibrium of such a game exists under mild conditions, and more importantly, it achieves the underlying efficient supply dispatch and the market clearing price that reflects the truthful system marginal production cost. Further, the mechanism can be tuned to guarantee self-sufficiency, i.e., taxes collected counterbalance subsidies needed. Extensive numerical case studies are run to validate the equilibrium analysis, and we employ individual net profit and a modified version of Lerner index as two metrics to evaluate the impact of the mechanism on market outcomes by varying its tuning parameter and firm heterogeneity
COPD identification and grading based on deep learning of lung parenchyma and bronchial wall in chest CT images
OBJECTIVE: Chest CT can display the main pathogenic factors of chronic obstructive pulmonary disease (COPD), emphysema and airway wall remodeling. This study aims to establish deep convolutional neural network (CNN) models using these two imaging markers to diagnose and grade COPD. METHODS: Subjects who underwent chest CT and pulmonary function test (PFT) from one hospital (n = 373) were retrospectively included as the training cohort, and subjects from another hospital (n = 226) were used as the external test cohort. According to the PFT results, all subjects were labeled as Global Initiative for Chronic Obstructive Lung Disease (GOLD) Grade 1, 2, 3, 4 or normal. Two DenseNet-201 CNNs were trained using CT images of lung parenchyma and bronchial wall to generate two corresponding confidence levels to indicate the possibility of COPD, then combined with logistic regression analysis. Quantitative CT was used for comparison. RESULTS: In the test cohort, CNN achieved an area under the curve of 0.899 (95%CI: 0.853-0.935) to determine the existence of COPD, and an accuracy of 81.7% (76.2-86.7%), which was significantly higher than the accuracy 68.1% (61.6%-74.2%) using quantitative CT method (p < 0.05). For three-way (normal, GOLD 1-2, and GOLD 3-4) and five-way (normal, GOLD 1, 2, 3, and 4) classifications, CNN reached accuracies of 77.4 and 67.9%, respectively. CONCLUSION: CNN can identify emphysema and airway wall remodeling on CT images to infer lung function and determine the existence and severity of COPD. It provides an alternative way to detect COPD using the extensively available chest CT. ADVANCES IN KNOWLEDGE: CNN can identify the main pathological changes of COPD (emphysema and airway wall remodeling) based on CT images, to infer lung function and determine the existence and severity of COPD. CNN reached an area under the curve of 0.853 to determine the existence of COPD in the external test cohort. The CNN approach provides an alternative and effective way for early detection of COPD using extensively used chest CT, as an important alternative to pulmonary function test
Effective adsorption of heavy metal ions in water by sulfhydryl modified nano titanium dioxide
Background: The monitoring and removal of heavy metal ions in wastewater will effectively improve the quality of water and promote the green and sustainable development of ecological environment. Using more efficient adsorption materials and more accurate detection means to treat heavy metal ions in water has always been a research focus and target of researchers.Method: A novel titania nanomaterial was modified with sulfhydryl group (nano TiO2-SH) for detection and adsorption of heavy metal ions in water, and accurately characterize the adsorption process using Surface-Enhanced Raman Spectroscopy (SERS) and other effective testing methods.Results: The maximum adsorption efficiency of nano TiO2-SH for the Hg2+, Cd2+, Pb2+ three heavy metal ions reached 98.3%, 98.4% and 98.4% respectively. And more importantly, after five cycles of adsorption and desorption, the adsorption efficiency of nano TiO2-SH for these three metal ions is still above 96%.Conclusion: These results proved the nano TiO2-SH adsorbent has great potential in practical water pollution purification
SAROTUP: Scanner and Reporter of Target-Unrelated Peptides
As epitope mimics, mimotopes have been widely utilized in the study of epitope prediction and the development of new diagnostics, therapeutics, and vaccines. Screening the random peptide libraries constructed with phage display or any other surface display technologies provides an efficient and convenient approach to acquire mimotopes. However, target-unrelated peptides creep into mimotopes from time to time through binding to contaminants or other components of the screening system. In this study, we present SAROTUP, a free web tool for scanning, reporting and excluding possible target-unrelated peptides from real mimotopes. Preliminary tests show that SAROTUP is efficient and capable of improving the accuracy of mimotope-based epitope mapping. It is also helpful for the development of mimotope-based diagnostics, therapeutics, and vaccines
Migration and Growth of Protoplanetary Embryos II: Emergence of Proto-Gas-Giants Cores versus Super Earths' Progenitor
Nearly of solar type stars contain one or more gas giant planet.
According to the core-accretion scenario, the acquisition of their gaseous
envelope must be preceded by the formation of super-critical cores with masses
ten times or larger than that of the Earth. It is natural to link the formation
probability of gas giant planets with the supply of gas and solid in their
natal disks. However, a much richer population of super Earths suggests that 1)
there is no shortage of planetary building-block material, 2) gas giants'
growth barrier is probably associated with whether they can merge into
super-critical cores, and 3) super Earths are probably failed cores which did
not attain sufficient mass to initiate efficient accretion of gas before it is
severely depleted. Here we construct a model based on the hypothesis that
protoplanetary embryos migrated extensively before they were assembled into
bona fide planets. We construct a Hermite-Embryo code based on a unified
viscous-irradiation disk model and a prescription for the embryo-disk tidal
interaction. This code is used to simulate 1) the convergent migration of
embryos, and 2) their close encounters and coagulation. Around the progenitors
of solar-type stars, the progenitor super-critical-mass cores of gas giant
planets primarily form in protostellar disks with relatively high ( yr) mass accretion rates whereas systems of super
Earths (failed cores) are more likely to emerge out of natal disks with modest
mass accretion rates, due to the mean motion resonance barrier and retention
efficiency.Comment: 12 pages, 5 figures, 1 table. Accepted for publication in Ap
Cross-border Acquisitions and Labor Regulations
Abstract Do labor regulations influence the reaction of stock markets and firm profitability to cross-border acquisitions? We discover that acquiring firms enjoy smaller abnormal stock returns and profits when targets are in countries with stronger labor protection regulations, i.e., in countries where laws, regulations, and policies increase the costs to firms of adjusting their workforces. These effects are especially pronounced when the target is in a labor-intensive or high labor-volatility industry. Consistent with labor regulations shaping the success of cross-border deals, we find that firms make fewer and smaller cross-border acquisitions into countries with strong labor regulations. JEL classification: G34; G38; J
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